What I think should have happened (feel free to add your own!)
Carrie:
Should have binned Aiden much much earlier, obvs. We could have done without the whole Aiden storyline, other than maybe a brief fling, where she realises that she doesn't love him at all and his family is too complicated for her, Carrie doesn't do families really. They could have shown her mid 50s writing career (which wouldn't involve a stupid mid century narvel) she could have been writing about dating and sex in your fifties / as a widow / fashion, anything but the stupid novel. The Carrie we knew would have furnished the house beautifully with a massive wardrobe and proper writing space. She should have met the downstairs neighbour naturally, as they shared a garden, without the stupid storyline about her shoes on a wooden floor. If he was going to be English, they should have left out the outdated stereotypes: pipe and mutton and writing about Thatcher, totally ridiculous. And Big should have been mentioned, as should her grief, do they think we've forgotten the whole love affair, marriage and death?
Miranda:
Should have been much more ruthless with Brady and his bloody sex life. I'd be fine with her deciding to be gay in her fifties but they should have left out Che (OBVS!) and the bumbling around not knowing how to talk to black people. Totally unbelievable. She went to Harvard! She was a shit hot lawyer! I'd have liked to see her navigating a legal career in her fifties. She also was a shit friend to Carrie in AJLT which she wasn't in the series. Also, Steve, I'd have thought they'd have had a better relationship after all these years, the dinner they had in the last episode where they talked about grandchildren was nice though.
Charlotte:
Massively underutilised. She's got a happy marriage, why didn't they show more of that? And the Rock stuff was irritating beyond belief.
Seema:
Underused. And not a substitute for Samantha.
Menopause - not mentioned, WTAF? Really?
Anthony, not enough of him
Stanford, never mentioned
Lisa TW - who cares
Nyah - likewise