Well, I finally caught up to the point where the Thirteenth Doctor regenerates. As usual, it seems to me that she's only just started being the Doctor. I think this must be a sign of age because when I was young it seemed that each Doctor lasted for ages, even the Sixth, but all of the new ones seem to me to quit after about six episodes. Which I know isn't actually the case, but still.
Overall I think that Whittaker has been easily the weakest of the new Doctors. I don't think this is her fault. She's a very good actor. The problem is that her Doctor, as written, simply doesn't have any gravitas at all. She's not really very charismatic and doesn't seem very strange, whereas all of the greatest Doctors have pulled off that odd combination of humour, compassion, authority, subversion, and alien weirdness and cold detachment. That's why Tom Baker is still the greatest Doctor, because that's what he's actually like, and why David Tennant is still the greatest of the new ones, because he understands it perfectly (and so did his writers). All of the new ones have managed it to some degree, other than Whittaker, which I suspect in her case is due partly to miscasting and partly to consistently very poor writing. (Also the dreadful wardrobe. Honestly, she was the worst-dressed Doctor of them all, and I'm including Colin Baker in that.) She did have some good moments, but they were few and far between. Compare Capaldi, who also suffered from a lot of weak writing and unimaginative stories, but who got the alien charisma of the Doctor down pat, had the chance to deliver some absolutely storming speeches, and enjoyed an unexpectedly excellent final season.
I think the real problem was that Chibnall was a bad choice for show-runner. The episodes he wrote were, at best, OK, and at worst were dull. Instead of crafting interesting stories and interesting problems for the Doctor he resorted to throwing in
every villain ever in ways that didn't generally make sense. His best episodes, such as
Eve of the Daleks, are those where he resisted the temptation to do this. On the plus side, he did cast Sacha Dhawan as the Master, who was absolutely superb. Also:
So he certainly wasn't totally terrible. Overall, though, his period as show-runner was weak, and it's a shame that that reflects, not entirely justly, on Whittaker - much as Colin Baker became the public face of John Nathan-Turner's poor direction.