I think the only changes made were to combat thralls specifically, and not all thralls in general. The patch notes reads “Re-balanced followers HP and damage across the board”, so it’s perhaps a bit ambiguous. I’m not sure if the changes also apply to pets, but I assume it does. Someone can correct me if I’m wrong, but I think any follower that has been placed before the patch is released will be unaffected by changes.
Minimal when the thrall was sufficiently leveled or if it was a quality thrall, but for some of the lesser thralls, some babysitting may be required to keep them alive at lower levels.
IMO, the reduction in thrall HP
I think they did a good job of balancing it. They reduced thrall HP and damage but also reduced world boss HP to shave off some of the grind associated with farming legendaries, while leaving normal world mobs mostly unaffected. Avatars were worked on, mostly to try to prevent exploits, but also to address some balance issues. It caused a slight change in who is the “best thrall” competition, but not enough to worry about unless you want to be in the top 0.1%. The balance changes were primarily intended to address PvE and group content. I don’t have any PvP experience in C.E. so I can’t answer to that aspect of it.