They technically do have mechanics, it's just now that people are level 20 (most? some?) and 3-5 magicites stacked into one slot, they're dying as fast as Hunt mobs.
NM's with the 'Thunderer' theme are comparable to the Hydra and Chimera Relic trials. The rest are comparable to dungeon bosses (low levels being mini-bosses and higher levels being final bosses)