I don't see the need for them to have moved away from the sort of mechanics we got in ARR and HW dungeons that involved things like luring a monkey to a banana tree, traps, mimics (fake treasure coffers), vents that increase damage if adds are on them, adds that spawn babies, etc.

But I do understand the fixed number of trash pulls. That was problematic before we had walls because tanks feel pressured to pull everything. So they pull everything, wipe, then everyone gets frustrated and potentially the tank or the healer feels like they messed up (when it was actually just too big a pull for what they could reasonably handle with that gear/comp/experience).