Yes it's really hard to make add a few variables that make mobs have less/more health, hit weaker/harder, have lower/higher resistances.
On easy mode servers you could have mobs die "fast" as the coblyns used to do.
On normal mode could be a decent challenge to kill.
Hardcore mode could be FFXI old style where you could need parties to actually kill something.
I'm not saying make different games on different servers. Just different difficulties.