Spoiler warning: Kara Danvers is Supergirl. Haha!
I agree and disagree with the thought that Kara revealing her dual identity to the world was not set up earlier. But it's arguable that it was set up as early as the very first episode of SUPERGIRL.
One of the weaknesses of ARROW: for the first several episodes, Oliver had nobody to talk to, so we had that ridiculous monologue until Diggle joined the cast. THE FLASH avoided this by making sure that as of the first episode, Barry Allen had a full support staff. SUPERGIRL did the same.
However, THE FLASH and SUPERGIRL both created a new problem with the instant support staff: the secret identity seemed utterly pointless. Aside from Iris and Cat Grant, every regular cast member on THE FLASH and SUPERGIRL knew that Barry was the Flash and Kara was Supergirl.
In both shows, the Flash and Supergirl seem to be putting in excessive effort to maintain secret identities to shield the truth from exactly one person, and when that person found out, somebody else became the shielded party. Iris found out The Secret, so Patty Spivot became the person who wasn't in on The Secret for THE FLASH's second season. Then THE FLASH decided not to bother having any regular cast members who weren't on the team.
SUPERGIRL from Seasons 2 - 4 focused on hiding The Secret from Lena Luthor after Calista Flockhart left. In Season 5, Kara's secret was hidden from William and Andrea. And aside from one episode in Season 4 where Supergirl changed into Kara Danvers' identity to seem like a helpless civilian when hunted by one of Luthor's thugs, the secret identity has been pointless. Why does Kara Danvers need a day job as a journalist? The original 1938 ACTION COMICS had Superman becoming a journalist so that he could learn about all of society's problems. That has been totally unnecessary since the release of the iPhone 3G in 2008; Kara could get the news without having to actually work in the news.
Why does Kara hide her identity as Supergirl when 99.99 per cent of the people in her life already know it? Why does Kara need a day job? Her Supergirl exploits are affiliated with the Department of Extra-Normal Operations, a federal organization that would have to pay her a minimum of $65,000 a year -- not counting all the money should could earn by donating fluid and cell samples for biological research for medical treatments.
When Kara got fired from Catco in Season 2, she didn't have any trouble affording her luxuries and supplies and home, partially because the show ignored the financial issues but also because even without Catco, she was still a federal agent.
Kara Danvers' civilian life is with her co-workers, all of whom are superheroes. Kara has absolutely no hobbies, pursuits or interests that would be impeded by becoming a celebrity in both identities.
The secret identity made sense when Kara was a teenaged girl, but since the first episode of SUPERGIRL, the secret identity has been totally unnecessary. The show is fully aware that it's completely unneeded with Lena Luthor outraged that Kara would have one.
I would agree that Season 6 did not really have a lot of episodes where Kara was wondering why she even has two separate identites when everyone she hangs out with already knows. But this has been a glaring peculiarity since the first episode of SUPERGIRL.
Season 1 played it as a psychological deficiency: Kara is a deeply insecure girlchild, Kara is nervous and socially awkward and intimidated whereas Supergirl is an identity where she can be assertive and forthright. But starting with Season 2, there was really no reason for Kara to have a civilian life.
I wonder at what point the finale was filmed. Was it before vaccinations became available? There wasn't the sort of distancing that BATWOMAN's second season had where Ryan Wilder couldn't kiss her girlfriend, so everyone was probably quarantined for two weeks prior to filming. And it looks like Calista Flockhart filmed alone. The one shot of her and Kara sitting together is a body double with hair obscuring the face.
I was... put off by some of the choices with Lena and Lex this year. Making Lena a witch is, as I said, a baffling choice for a character written and characterized as a scientist.
Giving Lex a love story with Nyxly is another odd choice given how the character has been written as self-serving and unsentimental with every expression of love having been a manipulative lie. Lex might have wanted Nyxly's power, but there was absolutely no sense onscreen that they had or could have ever had any kind of emotional relationship, nor did Jon Cryer or the scripts do anything to make Lex's love for Nyxly seem real. SUPERGIRL has on two separate occasions presented Lex as loving Lena as a sister or loving Eve Tessmacher only to reveal it was a trick. Saying that Lex wrote love poems doesn't explain how or why a self-serving sociopath like Lex could have actual romantic feelings or why Nyxly would be the recipient of those feelings.
Lena being a witch and Lex being in love didn't work for me. The totems... were a silly MacGuffin of nothing and aside from being something to fight over, I had no investment in them at all. There was a lot of drama over Andrea Rojas and her morality and I didn't really see why anyone should be invested in that character; she was just Kara's civilian employer. I found all the time invested in these story elements rather puzzling and not worthwhile.
I was also puzzled again by how Lex Luthor in the series finale was a physical combatant firing ray beams at superheroes. Is that really an effective use of Lex the master planner? Lex the manipulator? Lex, the man who took over America from his prison cell by using white grievance against aliens and people of colour? Is that really making use of what makes Lex Luthor unique and distinct from the average thug?
Overall, I enjoyed Season 6, but it was flawed in many ways, some unavoidable and due to unforced errors. Season 6 is actually best understood as two separate seasons: a run of episodes with limited appearances from Melissa Benoist followed by a run of episodes where she's back full time.
The Benoist-lite episodes were extremely well done, especially with the return to Kara's teenaged years. The superfriends friendships were vibrant and charming. There was a terrific exploration of how this team functions around Supergirl by having Supergirl absent. The Kelly/Alex and Nia/Brainy romances were extremely strong and Lena had a fantastic arc in defining her place when surrounded by superheroes.
But Supergirl's return to SUPERGIRL was rather weak: a rushed shot of Kara and Alex hugging, a token episode of Kara's father being thrown out of the series. Nyxly was an effective antagonist in the Phantom Zone, but she had no real rapport with Kara once on Earth, no course in the enmity and Lex was so un-Lexlike in his characterization this year that it might have been better to not use him at all.
While the individual episodes after Kara's return were mostly strong, the core plot of pursuing totems that somehow ensure all the good in the world was a clumsy shift away from Supergirl's technology-defined reality and into fairy tale magic.
Thankfully, the character arcs were still effective admidst this framework. I really liked the use of William Dey as an imbedded journalist and his end was tragic. I was very pleased with Kelly and Alex adopting a child, a note which also touched on why Alex and Maggie Sawyer broke up in Season 3.
I think that the second half of Season 6 suffered for a variety of behind the scenes reasons. There was no specific sense, it seems, of precisely when Benoist would be back on the show. There was no clear sense of what filming could and couldn't be done at that point as the pandemic protocols were continuing to evolve. There was clearly a lot of thought put into character arcs but there seemed to be much less thought put into the villains, their plans, the threats they posed and their reasons for their actions -- which led to magic totems and Lex being in love for Reasons.
I would have liked a seventh season of Kara Danvers, Celebrity Superhero. I'm not entirely sure why SUPERGIRL is cancelled, but the reality of every TV series is that every year, costs go up with salary increases while ratings go down with viewer attrition. In addition, SUPERGIRL was budgeted (and the actors paid) with the show to air on CBS and with the expectation of a tax credit for Los Angeles filming that didn't come through. The budget was cut and the show relocated to the CW with Vancouver filming, but it's likely the actors were still getting their CBS-budgeted salaries and annual increases as part of their original contract.
SUPERGIRL performed really well for CW with 3 million viewers for the Season 2 premiere; even the most viewed episode of ARROW had about 4 million viewers. By Season 5, SUPERGIRL was at about 65 - 90 thousand viewers; about where ARROW was for its seventh season. I'm not sure live viewing figures mean anything, however, as CW shows seem to draw most of their revenue from sales to streaming services. But THE FLASH, ARROW and LEGENDS didn't start on a CBS financial model. SUPERGIRL did, and it's likely that Season 6 was the last because it had reached the point where its sales no longer justified the next round of CBS-contracted salary increases.
It's interesting how we have come to expect endings to TV shows. In contrast, shows up to the early 2000s were produced for indefinite renewal with conclusions / cancellations only known after the final episode had been filmed. It was rare for writers to know in advance and script accordingly. This was viewed as an unfortunate reality of how the TV business functioned.
But today, a conclusion is expected. A failure to provide one is viewed as mismanagement. If a show gets cancelled without an ending, studios and networks are called upon to order 1 - 2 more episodes to offer a finale. Shows without endings are not suited to streaming services. There was some chatter about how Netflix staff were upset and embarrassed at the bad publicity that came with cancelling LUKE CAGE, IRON FIST, THE SOCIETY, I AM NOT OKAY WITH THIS, TEENAGED BOUNTY HUNTERS, GLOW, DAYBREAK, SANTA CLARITA DIET; for the TV show TRINKETS, they renewed it for Season 2 but advertised it as the final season to avoid such issues. The CW did the same for SUPERGIRL, renewing for Season 6 but stating in advance that it was the last season. It's a shame that the pandemic and Benoist's absence made it hard to plan better.