The tail-end of SUPERGIRL's third season is *weird*. There is no sense of what the Season 3 plots are really about beyond Kara wandering around fighting three supervillains; there is no clarity as to what the new characters of Season 3 represent beyond their immediate plot purposes.
Season 1's Kryptonian invasion arc was about Kara trying to reconcile her anxiety and need to be more assertive: assertiveness sometimes comes out as destructive anger or the inability to work with others and Kara has to find the right balance.
Season 2 was about how women support other women (and sometimes men) and sometimes fail to: Queen Rhea supports no one and nothing but guises her selfishness in the language of female empowerment; Lena supports everyone and everything but has trouble trusting and being trusted; Supergirl thinks supporting people is to assume they're just like her and has to learn to accept and embrace difference.
Season 3 started out with the theme of Kara starting to lose touch with her humanity, taking on the inhuman Worldkillers who have no humanity -- and then it just degenerates into superhero plot points without having much to say about what it means to be human.
The reason for this is pretty obvious: showrunner and unrepentant sexual harasser Andrew Kreisberg was well-deservedly fired from SUPERGIRL for unrepentant sexual harassment of his writers. He was off the show by Episode 3.12 and the remaining episodes of Season 3 come off as a novel where the original author died after writing half of it and the second half was written by someone else who had no idea where the story was supposed to go.
Unrepentant sexual harasser Andrew Kreisberg introduced Samantha Arias and her daughter Ruby. Sam is a childhood friend of Lena's; Sam is a single mother; Sam is L-Corp's new financial officer; Sam is unknowingly a genetically engineered Kryptonian Worldkiller sent to 'purify' the planet Earth. Unrepentant sexual harasser Andrew Kreisberg also brought Mon-El back but this is a Mon-El who's lived seven years since Season 2 and is now married to Imra, the telekinetic superhero Saturn Girl from the 31st century. Unrepentant sexual harasser Andrew Kreisberg set up some mysteries: what is the Worldkiller's purpose on Earth? What are Mon-El and Imra's reasons for coming back to 21st century Earth?
Unrepentant sexual harasser Andrew Kreisberg got fired before he could bring these plots to a conclusion. The answers provided by his successors suggest that they didn't know what unrepentant sexual harasser Andrew Kreisberg had planned. Some have speculated that unrepentant sexual harasser Andrew Kreisberg had left outlines that his successors refused to use in order to avoid paying him any further story or teleplay fees, but the awkwardness in resolving the Season 3 story elements suggests that their ex-boss was too busy harassing them to provide them with his plans.
Sam Arias unknowingly transforms into Reign, a Kryptonian Worldkiller whose powers are... the same as Supergirl's except Reign beats Supergirl to a pulp and is presented as stronger. All well and good -- but what exactly is the purpose of the Worldkiller? It's said that the Worldkiller is to "purify" the Earth for Kryptonians by brutally murdering criminals -- but what's the endgame after Reign has presumably killed all criminals?
Other Worldkillers include Purity and Blight who seem to be more interested in clearing all humans off Earth through physical violence -- but why? Surviving Kryptonians in Season 1 lost interest in Earth. Later in Season 3, Kryptonians are shown to be perfectly capable of creating new settlements like Argo City. And even if Kryptonians wanted to extinguish all human life, they could use Myriad's Q-waves to shut down all human brains.
By comparison, three super-superpowered Kryptonians punching humans to death one by one is highly inefficient.
It's unclear what these Worldkillers are meant to accomplish. The Season 3 writers seem to have no idea what the Worldkillers were supposed to be and Mon-El and Imra's secret mission to stop the Worldkillers' plan of something or other is just baffling.
The Sam Arias character is also awkward. Unrepentant sexual harasser Andrew Kreisberg was strangely sloppy in introducing this new character in Season 3. Sam is described as a childhood friend of Lena's in the same episode where Lena says that she's never had any friends. Sam is an accountant and defined by constantly walking into rooms describing how she just accomplished some vague financial goal for Lena at L-Corp. Sam is suddenly in Kara Danvers' circle at the weekly game night and Kara is talking to Sam like they've been friends for years when, to the audience, Sam is a stranger.
It's hard to get a read on Sam's character because Sam's role on the show is to spout vague business terms and be present in mother-daughter scenes with 12 year old Ruby. Is Sam cunning like Oliver? A people person like Iris? Relentlessly practical like Diggle? A problem solver like Mary? An agent of chaos like Kate Kane? No idea, the show never presents Sam as anything beyond a mother.
Unrepentant sexual harasser Andrew Kreisberg doesn't know how to define Sam and doesn't know why Lena and Sam are friends. I can't tell if Sam is cunning or clever or full of empathy or who this character is beyond being a loving mother.
It's almost as though unrepentant sexual harasser Andrew Kreisberg simply had an infatuation with actress Odette Annable and wrote a role for her; Sam's human persona is almost irrelevant beyond being Ruby's mother. Sam is simply the human face of Reign like Davis Bloom was for Doomsday in SMALLVILLE -- except Davis Bloom had characterization: he was a paramedic (and so relevant to superhero combat situations); he was assertive and compassionate but with a dark anger.
In contrast, it's hard to pin down anything about Sam and the character only functions because Odette Annable can infuse her own humanity and warmth into the role. Sam is a pleasure to watch because Annable is great, but Sam is a non-entity.
After unrepentant sexual harasser Andrew Kreisberg was fired, the post-Kreisberg writers elected to focus on the Reign persona and mostly kept Sam locked in a hospital bed or dreamscape until Supergirl could save her. Then Sam and Ruby were written out of the show.
Ruby Arias is also written pretty vaguely but adequately. She's an insecure but kind 12 year old girl and she and Alex Danvers form a bond as Alex babysits and protects her from Reign. Alex seeing Sam and Ruby together makes Alex realize she wants to have her own children.
What were unrepentant sexual harasser Andrew Kreisberg's intentions for Sam and Ruby? It was reported that Odette Annable was signed for one season, but Ruby's actress, Emma Tremblay, was signed for two years. It seems Kreisberg meant to kill off Reign and Sam and have Alex adopt Ruby. The writers seemed to find this too brutal and instead spared Sam, eliminated Reign, and sent Sam and Ruby off to happy endings.
Towards the end of Season 3, the writers clearly realize they can't wrap their heads around the Worldkillers, Sam, Reign, or Ruby. At the same time, they have to keep spinning their wheels with these elements until the Season 3 finale.
As a result, the writers decide to focus on something they can appreciate: they focus on the Kara and Lena friendship. They have Lena and Supergirl at odds over Lena having Kryptonite and other anti-Kryptonian armaments that Lena uses to fight the Worldkillers. The shift in focus to Lena and Supergirl at odds while Kara remains Lena's best friend is amusing, bizarre, funny and painful.
It's utterly detached from the Worldkillers; the Worldkillers are defined by a rejection of all emotion and compassion and relationship, in some ways reflecting Kara's emotional distance at the start of Season 3. The Lena/Supergirl/Kara conflict, however, isn't about emotional distance but emotional entanglement where Kara, Supergirl and Lena find themselves at times unknowingly battling different sides of their best friends.
The Kara/Lena focus works very well. There's a hurtful moment when Supergirl tells Lena that she's sorry for getting upset with Lena over Lena's anti-Kryptonian weapons and hopes they can still be friends; Lena disbelievingly snaps that they've never been friends and has no idea why Supergirl thinks they've ever done anything but work together.
It's a hilarious inversion of the SUPERMAN movies where Superman always makes a point of not recognizing the name "Clark" whereas Supergirl constantly forgets that people who are close to Kara may consider Supergirl a stranger.
The post-Kreisberg writers seem to have no idea what the hell unrepentant sexual harasser Andrew Kreisberg was doing with Season 3; the post-Kreisberg writers are awkwardly trying to turn SUPERGIRL: THE WORLDKILLER WAR into SUPERGIRL: KARA AND LENA.
The post-Kreisberg writers feel better equipped to write KARA AND LENA. They're excited about KARA AND LENA. They're passionate about KARA AND LENA. And they're just grudgingly working through the last episodes of THE WORLDKILLER WAR until they make it all Kara and Lena all the time in Season 4.
It works out beautifully in Season 4 -5, but Season 3 is truly awkward in changing course.