Suggestion (Required)

Can you give the marauder a melee attack when at close range to the player?

Mabey you could also make alchemists immune to potion affects because if there are many of them in a group and they are trying to attack 1 target they end up poisoning each other. and/or let them heal themselves with potions?

Added in v21.3.0. When you get closer than four blocks they will switch to a melee attack and run after you.
For alchemists; they are immune to poison in general, which works fine for the potions they throw themselves. But I have noticed myself that they do sometimes get poisoned from other alchemists. I assume that's a vanilla bug.