I don't use mods, but even if I did, I'm thinking specifically of the Unbound Abomination - final boss of the Underrot in BfA. This guy can't be conventionally damaged - you have to beat on him until a secondary "blood gauge" fills up, spawning adds you kill to actually damage him. He also puts a persistent, stacking DoT onto the party which a helper NPC will periodically cleanse in an AoE around a random party member, and also puts down randomly placed, persistent AoE patches around his boss room that will very quickly kill you if you stand in them. That's just on normal. Hard mode (Mythic difficulty) has those AoE patches turn into mobs that track players, which when killed put their patch back down until they get up again.
This is a 5-man dungeon boss. Admittedly the most difficult one in the expansion, but there's nothing of comparable difficulty in XIV beyond some high-level 2.0 dungeons (Dzmael Darkhold and Aurum Vale). Everything here is learning the boss's telegraphs and dodging, stacking, or spacing as necessary. It's certainly easier, and more convenient, but less fulfilling.