Was Hell Bent one return too many for Clara?

I've actually had the opposite problem. After the first year and a half, I found that they were always what I expected. The only two stories to really shake that monotony were The Witch's Familiar (aided in no small part by the delightfully mad Michelle Gomez) and Heaven Sent (I wish the whole season had been of the same quality). I can't help but feel if we'd had more stories like the aforementioned Heaven Sent, Vincent and the Doctor and The Snowmen, I would have looked back on his run more fondly.

It didn't help that Clara degenerated into a very, very irredeemable character that sits squarely in the Mary Sue category. Which is sad really because there were glimmerings of classic companion dynamics buried deep beneath. What if Bonnie the Zygon hadn't been a duplicate, but instead just the regular Clara? A female Avon who the Doctor was trying to re-educate? What happened to her neurotic behaviour in Deep Breath[? Wouldn't that have been amazing? Despite Jenna Coleman's best efforts she is smug, selfish and so thoroughly unpleasant as to rival TV!Adric.

This is entirely my opinion, but I think that the Moffat production office definitively hit burn out halfway through Matt Smith's second year. You get to Let's Kill Hitler (awkward for me personally because I was reading Just War at the time) and the Doctor becomes largely irrelevant, the River arc is extended long beyond its due by date and out in the real world, many friends of mine stopped watching the show in droves. I've noticed many of them started watching the classic series and came back to NuWho feeling it was a bit lackluster (although one of them is still hanging in there with Capaldi, even if his opinion of the Twelfth Doctor is sadly not very high).