The only problem with that for some is that there's no bonus or benefit for the kill. You could do 95% damage then leave the boss for the other team, knowing you've got the points, and they have to risk their lives to kill it.

Ultimately, whatever mechanic s set up, it is fundamentally fair because both teams have to employ the same strategy and deal with the same mechanic. So the question is - what boss mechanic is most satisfying to most of the gameplaying community, not what is more "fair" or "competitive'. Hopefully though, what is most satisfying to the community is that which is most fair and competitive :) Minimize potential frustration while maximizing potential win-highs, whether you're winning or losing.