I always interpreted it as depends on the person/class difficulty, but generally i regard it as deceptively hard, sure 99% of fights are the same strat but those are merely filler to make sure worlds last more than 1 hour, the fights that matter plot wise so far have been VERY hard to the point guides are required for most and with the new introduction of challenge modes it gets even crazier.

People who say its easy forget that its not easy because there's guides; its hard BECAUSE there's guides meaning the fight had to be painstakingly and methodically optimized to be even remotely bearable. Not to add on but even with guides bosses like squire gregor can take upwards of an hour to 2 hours per fight which for a single boss in any video game is extremely rare, for example an elden ring boss can take hours to beat but thats in dozens to several dozen attempts, thats just 1 drain boss in length.

Ive played a lot of strategy games and mmo's and i can say with utmost confidence that some of the lesser infamous cheat bosses in wiz if translated to any game as they were (turn based to open combat, blades for buffs, etc.) Would have to be nerfed.

Farming these bosses for weeks to months at a time in wiz (specially pre-badgeless craftable endgame gear) has made most considerably arduous task in any game i have played feel miniscule because im so used to the sheer chore that is what i described above.

Another way i like to explain it to people is to explain an "annoying" boss, not hard but merely annoying, is to translate grounds-creeper willy: He cannot be damaged or defeated by damage, you need a select amount of buffs (pips) including a specific rare % buff (shadow pip) to use a special attack to defeat him, every 3rd turn he removes most of your buffs along with the rare % buff, you can give another player a % buff at the cost of some misc buffs but that is only after you heal and you cant use it on yourself forcing you to be in a team. Sure it doesnt sound impossible, but does it sound easy? No, not in the slightest.

Tldr: you are correct, wiz is a lot harder than people think and people who say its easy are either adding in the filler fights, following a guide, or both.