Regarding the killquest change:
I'm pretty fine with the actual killquest counter, can use it to replenenish SP or reapply buffs(if using external). Also the out-and-in doesn't even take a minute so idk.
But if you'd change the quests, then why stop at varmundt? With the given argument ("breaking flow") the killquests, if changed, should be changed for all farmable stuff.
Though probably not everyone wants to commit to kill 500 mobs a day to get the questreward. Maybe afloating killcounter would be a feasible solution to that. So it just tracks the amount of kills until the next time you speak to the NPC and the npc will give you rewards according to you killcount (i.e. 627 kill == 6x Reward up to 15 rewards perday)
But in the end thats maybe too much effort for so little inconvenience.
Regarding mob hostility:
some biospheres maps feel/are worse than the others to farm.
i.e.
grass>passive mobs
soul/temple>mob density/element diversity?
So it's usually more efficient to farm something like ice/fire/death instead of grass/soul.
I agree that making all mobs agressive would solve some issues but i'd also suggest increasing the mob density on some of the worse maps (looking at you soul) to make them somewhat equal in comparison to the high density maps.