They invariably didn't. They were useful in the peaks and on Sundays but it was absolutely typical to stand at Leicester station and watch the 4 or 5 car ex Sheffield semi fast leave full and standing after everyone had wedged on (we quite often didn't have a single seat left especially in first) and then a handful board the HST 5-10 minutes behind on the ex Nottingham fast.
They were used entirely for operational convenience and they weren't much better heading north.
Comfort is subjective - for everyone who liked the old style interior there was another person who hated the fixed armrests and lack of plug sockets in standard while getting covered in muck opening the doors. The LNER sets are better but you now get people wanting the old EMT interior sets back so you can't win
I've spent most of the last decade working in a front line role in the area of the MML and I can tell you that both 222s and HSTs were marmite - but that more regular passengers asked after the 222s for their more modern facilities on offer.