The Jodie Whittaker and Chris Chibnall era ends with... a very okay episode. "The Power of the Doctor" was fine.
An Action Writer Writing a Woman of Inaction
I think what sums up Chibnall for me: he's an action writer. He writes stories driven by fight scenes. This is fine if you're writing MACGYVER, SUPERNATURAL or even SLIDERS; it's a serious handicap when writing post-2005 era DOCTOR WHO. Since 1985, the Doctor has generally been a science hero who outthinks and outsmarts villains; the more violent versions of the character haven't been around for decades.
Chibnall clearly thinks it's inappropriate to have the Doctor throwing punches or firing guns except in isolated circumstances. Therefore, Chibnall... generally has the Doctor standing by while her allies fight because the Doctor is immobilized or passively present; alternatively, the Doctor's passivity leaves her overpowered and defeated until other characters rescue her.
The Doctor -- and the sliders -- can be difficult to write. Even the great Tracy Torme struggled and sometimes flat out failed. "Luck of the Draw" from Jon Povill has the sliders using cleverness to escape and defeat their antagonists, but immediately with the next episode, "Into the Mystic", Torme's script has Rembrandt wielding a shotgun while Arturo attacks and overpowers sorcerers and security guards.
Russell T. Davies had the Ninth Doctor often stand around while guest stars sacrificed themselves to resolve the episode. He clearly regretted this because the Tenth Doctor was far more prone to using machinery and technobabble to remove enemies. The Tenth Doctor using a gun in his finale episode was presented as a moment of severe wrongness. The Eleventh and Twelfth Doctors were much the same except Steven Moffat was better at establishing his machinery and technobabble earlier in the story to deploy at the end.
Why not write a more aggressive Doctor?
Chibnall doesn't write the Doctor's pacifism effectively; in Chibnall's hands, pacifism is passivity. Chibnall is clearly more comfortable writing the Fugitive Doctor because the Fugitive Doctor is prepared to use violence while the Thirteenth Doctor won't.
The thing is, while most-2005 and onward fans know the Doctor as a pacifist, that's not the case for all Doctors. The Third Doctor was a gentleman spy who used martial arts. The Fourth Doctor did not hesitate to use violence but found it distasteful and grim, preferring humour and charm. The Sixth Doctor was downright aggressive against enemies.
The First Doctor was originally prone to fisticuffs until his characterization became more grandfatherly; the Second Doctor was a trickster, the Fifth Doctor was a non-violent diplomat, the Seventh Doctor was a master manipulator who used indirect means, the Eighth Doctor was a non-violent improviser, and aside from the War Doctor, Doctors Nine through Twelve were generally pacifistic except for the Twelfth throwing one angry punch in one episode.
Chibnall could have absolutely made the Thirteenth Doctor more like the Third, Fourth and Sixth Doctors, prepared to use weapons and martial arts.
Chibnall is clearly more comfortable writing the Fugitive Doctor, a Doctor who grabs weapons, punches enemies, tricks villains into shooting themselves. Chibnall wouldn't write Jodie Whittaker in the same vein.
Sugar and Spice and Everything Nice?
Did he feel too tied to the more recent presentations of the Doctor as a non-violent thinker? Did he feel Jodie Whittaker's presence was mismatched to more aggressive action and occasionally deadly intent?
Did he think the first female Doctor needed to represent women as non-violent and vulnerable and nice as opposed to hard-edged and combat ready?
For whatever reason, Chibnall chose a Doctor-character template that just wasn't in his skillset. Chibnall is not the sort of writer who comes up with impossible circumstances and then drops the Doctor/Quinn/Arturo into the situation and lets them piledrive through the problems.
Chibnall is a procedural screenwriter who creates problems and devises solutions within a formula that is resembles a cop show (BROADCHURCH) or a science fiction action show like STAR TREK. Chibnall's stories need his hero to use force and violence; he wouldn't do that with the Thirteenth Doctor and it clearly crippled him.
Chibnall's Doctor was thinly defined. In the finale, characters talk about how the Thirteenth Doctor is strong and heroic, Jodie Whittaker's performance seems to think that she is. But the Thirteenth Doctor is defined by standing around while the plot happens.
I can't imagine Matt Smith sitting in a cell waiting to be rescued by Captain Jack, but that seems to be Thirteen's defining moment. And because the Thirteenth Doctor was so vague and contradictory, none of the companions ever solidified.
Ryan, Graham and Yaz were simply scene partners for the Doctor to address and explain the plot; aside from Ryan being informal, Graham being older and Yaz being female, none of them cohered as personalities. When the Doctor has no identity, the companions have no clear purpose in how to support that identity. In contrast, the Eleventh Doctor was a childish goofball while Amy and Clara were ball busters; the Fourth Doctor was madcap while Romana was calm; the Ninth Doctor was tormented while Rose was passionate.
The Thirteenth Doctor was just vaguely nice -- which, I guess, brought us to a Thirteenth Doctor finale where she is incapacitated and has to be bailed out by the First, Fifth, Sixth, Seventh and Eighth Doctors.
Why these Doctors?
There is no particular in-story reason why the First, Fifth, Sixth, Seventh and Eighth Doctors show up as opposed any of the others. From a writing standpoint, one would think that the Thirteenth Doctor's psyche would be populated by the nicest, gentlest Doctors: the Second, Fifth, Seventh, Eighth and Eleventh.
Alternatively, the Thirteenth Doctor would be confronted by the aggressive sides of her character that she'd set aside: the First, Fourth and Sixth as well as the War Doctor and the Ninth and Tenth Doctor.
A more artful writer would recognize that the actors available were David Bradley, Peter Davison, Colin Baker, Sylvester McCoy and Paul McGann -- and find a psychological rationale. The First Doctor could be the Doctor's wanderlust, telling the Thirteenth Doctor that she has so much more to see. The Fifth could be the conscience, saying the Doctor can't allow her body to be misused and must fight even if fighting to lose. The Sixth could be the determination, urging the Doctor hold steady and wait for a chance. The Seventh is the strategist, crafting a plan. The Eighth is the Doctor's love for life and friendship, telling the Doctor that she won't be ready to let go until she sees Yaz one more time.
Instead, all the characters get nicely Doctorish dialogue that could have been delivered by any Doctor. Colin Baker, the meanest of the Doctors, is written to be as gentle as soft-spoken Peter Davison! (Admittedly, the Colin Baker is indeed the nicest one.) Chibnall is a professional who does a professional's job, but he doesn't capitalize on the opportunities he has.
Another missed chance: Chibnall nonsensicially waited two episodes before the Thirteenth Doctor was leaving to address Yaz having romantic feelings for the Doctor and the Doctor feeling the same way but choosing not to pursue it because Yaz would age and die and the Doctor would regenerate.
The finale does a rather sweet job of handling this undercooked plot, however, with Yaz silently loving the Doctor and mourning this version of her and choosing to leave before the Doctor she loves becomes a new version, but Chibnall's undercooked, underdeveloped characterization remains a sore point. It's still baffling to me that Yaz and the Thirteenth Doctor have been on this show since 2018 and that Chibnall waited until 2022 to acknowledge the romantic tension.
Chibnall did a decent job with the Fifth Doctor (Peter Davison) and Tegan (Janet Fielding) having a last conversation. Chibnall also did a very nice job with a small exchange between the Seventh Doctor (Sylvester McCoy) and Ace (Sophie Aldred). Chibnall flat out contradicts the one audioplay featuring Davison and Fielding as their characters reuniting in 2006 and the one novel written by Sophie Aldred where Ace met the Thirteenth Doctor, Graham and Yaz. This is understandable as the majority of viewers aren't familiar with "The Gathering" audioplay or the "At Childhood's End" novel.
Ultimately, "The Power of the Doctor" is a functional, professional, adequate story with some pleasant moments where the Thirteenth Doctor is a passive passenger in her own story and where every chance for drama is mined professionally but minimally with a very moderate, adequate, unspectacular level of drama or humour. It's mildly enjoyable and sufficiently diverting, but the most memorable and gripping moment is at the end when Jodie Whittaker dies and regenerates, only to find she's somehow become David Tennant again for reasons unknown.
The Ending Wasn't Chibnall
Tellingly, this massive shock had nothing to do with Chris Chibnall. When Chibnall scripted "The Power of the Doctor", there was no word as to who would be the next showrunner or if there would be another season; it was unlikely the BBC would cancel DOCTOR WHO, but it was possible that anywhere from 1 - 3 years would pass before the show would return. Chibnall ended his script with the Thirteenth Doctor regenerating; incoming showrunner Russell T. Davies scripted the next page with the Fourteenth Doctor astonished to find he's somehow become the Tenth.
It's rather revealing that most significant development of Chris Chibnall's finale episode was the one page Chris Chibnall didn't write.