I've just recently found this forum and hope you don't mind my entering the discussion.
The evolution of a TV series is an interesting process. At the beginning, as the characters are being formed by both the writers and the actors, we simply take them in and decide what we think of them. The writers and actors have free rein with what they will do. And then, at some undefined time, the character is deemed (by us) to be fully formed, and we begin to measure their behaviors on screen against what we would expect of the people they've been written to be.
For series with consistent writing teams, this can be a seamless process. But, when there is such overhaul as there has, apparently been with CM (I'm a latecomer, discovered the series through syndication), there is inherent room for the new writers to stray far afield from the characters as they were originally written. This is often dismissed as 'character growth', when it really represents a misunderstanding of the character by the new writer.
In the case of CM, I think this has, indeed, occurred. I've had a condensed experience with the series, and can see that there is a marked difference between the original composition of each character, and how they are currently represented. Similarly, there was an intelligence and, importantly for me, a pathos, that infused the series. The intelligence tries to rear its head from time to time these days, but the pathos is almost completely gone. We saw a hope-inspiring remnant of it with Reid's reaction to losing Maeve, and the team's reaction to him. But I have to agree with those who think that the pathos has been lost this season, and I also agree that the whole miswriting of the 'curing' of Diana is the best example of it. (Totally ignoring the very existence of '200', now and forever).
Reid's relationship with his mother, and Diana's mental illness, were two of the best established 'personal' themes of the show. To simply dismiss both of them with a miracle cure was, I thought, evidence of writing that just felt immature to me. As though the writer didn't understand the dynamic, or the importance of it, and was willing to give it all away for a 'cute moment' at the end of the story.
Or maybe it simply reflected a lack of imagination on the part of the writer (and the whole writing team---I've read that they vet the story lines with each other before proceeding). They seemed completely nonplussed by not having Jane Lynch on the show. How hard would it have been to have Reid receive an out-of-the-blue phone call from his mother, to celebrate a new improvement in her mental health? Just watching his end of the conversation, trusting MGG to come through on the acting end, would have been priceless. If they couldn't manage that, then just show him frustrated by being too busy to see his mother while in Vegas. Even simpler, avoid Vegas completely. Or was the episode set there specifically so they could 'amend' canon?
If CM hadn't ever had its day in the sun, I would certainly not have been moved to create this annoyingly long first comment. But it did have its day, and it stood head and shoulders above other series By choice, I will remain hopeful that it can go out the same way.