It's kinda sad to read what players understand under trash mobs.
If you compare it with other ffxiv trash mobs from previous raid tiers then yeah, it would be pretty boring.
If you add unique mechanics and random item drops to trash mobs, they could indeed make a raid feel more climatic and atmospheric.
Other games save the ID progress, e. g. number of mobs you killed, etc. So if you requeue you won't have to do it again.

I doubt though that SE will change something about the story(solo dungeon) mission for raids like we experienced for omega. As long as they exist we will get a circle map with a HP sponge in it, that we have to beat with raw dmg over time while performing a mechanic dance instead of having an actual mechanical victory (not failing mechanics grants a buff or debuff to kill boss faster like ucob last phase as rough example) The only way this game works in 99% is punishment, if you do bad you get a disadvantage, why not tune bosses other way around. If you do good, give us advantages to kill it faster.