So this might sound pretty obvious, but I think that making a boss/mob spawn more frequently if there are a lot of people in an area would be great. I keep seeing bosses with like 30+people surrounding its spawning location, having the boss spawn every like 15mins, and getting 1shot making a lot of people unable to finish their quest.
Another solution would be to buff bosses depending on how many people are around it. This will make sure that it doesn’t get 1shot letting everyone at least hit it once, and is a great way to balance the games difficulty between solo and group players.