Not that map bosses have ever been "balanced" for tier difficulty and so forth, but the new bosses of maps seem to have all been tuned up across the board and all the new bosses seem at the difficulty level at least of the hardest bosses in the past. Been running 5-7 tier maps mainly atm and the tuning seems kind of over the top.
In general, it seems almost all of the easiest bosses are gone (or moved up to higher tiers), with all the new bosses doing tons of damage or having tons of hitpoints (and usually both at once). Also quite a few more mechanics that if you ignore will kill you (racecourse 100% reflect aura that the horse dude puts up). We aren't talking about a 10% to 20% buff to boss hitpoints, no, many bosses seem to have multiples of their earlier health.
I mean, whatever, I'm dealing with it. It just seems a silly thing to do so early on in the mapping. PoE was never a particularly friendly game towards new players, but with my build doing really high dps and ignoring mob resistances, it still takes me quite a long time (relatively) to kill many of these bosses.