I really really hope that with "balancing changes" you don´t mean that they will get easier?! This would ruin the experience. Me and (as much as I have read on social media) most players find that these bosses were actual really good! If I should say one thing that the expansion made better than the main game, it was for 100% the balancing of the bosses! They are strong and challenging, if a few people find that they are too hard, they shouldn´t maybe play on Death March
If there is one single boss that is maybe sometimes a bit "bugged" (I wouldn´t say "too strong" or "op) it´s the caretaker, because sometimes he gets into a loop where he stuns you and heals up to full life, by killing a few ghosts. However most people beat him after a few tries. Finneas fist fight was way harder in comparision to that fight
Instead of that you could maybe make Eredin harder, because most people beat him after first try, even on Death march
If someone was too lazy what I wrote, this guy sums it up pretty well: