Let's do a comparison.
Sabotender Carrido in Anemos has:
-Raid Aoe
-melee aoe around it
-targetted aoe
-stack marker
That's it. That's literally open world mob level mechanics; you can even argue its literally a cactaur mob given a stack marker. Compare the very first, weakest Critical Engagement, the Mandragora thing:
-Raid Aoe
-stack marker
-tank buster
-Multi-person targetting aoe that unleashes 3-4 sets of aoes back to back
-Managing a color debuff that will one shot or deal incredible damage if you don't swap colors on each set, along with making sure you're not standing in the black insta death zone.
-Dodging a constant rotating carousel of adds from the outside rim that spew hearts that need to be dodged or they deal high damage + confusion, putting you in a vulnerable state for the ground aoes, the color mechanic, etc.
Well over half of the Eureka bosses were literally just normal, open world mobs given 1 extra mechanic. The only ones even comparable to Critical engagements were the ones close to the zone's level cap, and even then a lot of them are super forgettable. This is even before the fact that Castrum's & Dalriada's bosses are basically on the same level as 24 man raid bosses in terms of mechanical design. That's also disregarding the duels that are leagues above anything in Eureka outside of Ozma in terms of mechanical design & complexity.
Let's not keep our rose-tinted glasses on. Eureka had quantity in bosses due to more zones; whereas Bozja's bosses are much higher quality in fight design. There was even the fact a good majority of Eureka's bosses weren't even threatening if you were a caster or ranged, since half their mechanics couldn't even affect everyone at the NM due to the game's internal target limit on enemy attacks when you had like, 100+ people all targetting the poor thing.