I really do think the hamming was the fault of the script - I’ve seen him perform entirely differently in other productions. (unlike Tenant who seems incapable of doing “subtle” in anything and was rather well contained by the early scripts).
Otherwise I agree with most of your points, including wanting the big love to come back.
This post reminded me of @SheilaFentiman ’s It's a bit of a rock and a hard place for the showrunners - too much focus on sexism or racism and Dr Who is 'woke' - not enough and it's unrealistic!. which I meant to come back to.
I’ve no doubt that the white MC male dominated Beeb would say exactly that. I have no sympathy with that viewpoint's hierarchy of representation - as someone who ticks quite a few of the EDI boxes, both inborn and acquired, I could tell you that the culture behind the story telling and writing is white male MC without looking at the team.
The hierarchy typically prioritises areas which are of no risk to or actually benefit the dominant cultural group creating the content. So sexuality, gender support - also benefits some MC white men and just happens to get disproportionate representation (and tragically bad casting in some cases). Some ethnicities are included whilst others are completely overlooked (how many East Asian or Jewish major characters in this mostly UK city based drama?) Coverage of women is often ambivalent. I don’t even think its deliberate or even conscious quite often, its simply what happens when the dominant group determine coverage. The pious lecture mode for those of us too thick to get the righteous point just grates.
I agree with @Snapespeare that hammering on about visibility is inconsistent with actual representation if the characters remain background characters. That said you want a blend of background, supporting and occasional leads. I thought the Rose Ayling episode was masterful - brilliantly written, the disability was relevant and she was a key character in the story without being what the story was entirely about. I felt the same about Dot Bubble.
I’d also call out small moments such as Belinda taking the doctor to task for the Doctor mansplaining to her and scanning her without consent - those small moments are “good” diversity writing, largely because they simply flow without RTD putting a neon sign over them to virtue signal.
Overall like Snapes I want to love it again and part of my frustration is because sometimes they get it so right that I feel they should be getting it right more often (and drop the bloody lectures).
I also am annoyed at the early loss of Belinda and Archie’s Rani. Two brilliant actors/characters wasted.