3k hps at 30 damage per hit is 100 hits. 5 players 20 hits each, each player having 250hps means each player takes 5 hits from a mutant bear for a total of 20 hits between them.

This seems balanced to me towards your goals of wanting it to be a multiple person fight.

Sure one guy with 350hp like ddt could solo it with maybe 80-100 hits but he could only take 7-8 hits himself so he would need to heal multiple times in order to get all 80+ hits on the bear to kill it, yes its possible, but its only possible cuz his hp pool is so high to go in, hit n get hit, run n heal, than go back n attack it again... it would take at least 5+ heals for someone to solo a bear like this, its really not something people can solo without heavy hit and run+heal abuse.

So damage is not the problem here when nobody can become stronger than a regular deer or bear... again the reason why the health is so high is cuz you've stated your goal to be that it requires multiple people to kill it, this naturally requires a bigger hp pool if you truly want to make it a "boss"