Ah yes... HP increase would mean you have too do more evasion tactics, and trap placements, and rely heavily on your friends (I.E. Teamwork), and aid your friends in some form or other too increase the oddsSounds like Survival Mode and Fire Fight horribly mixed up.
What is the objective if your HP gets increased ?
If that was made into PVP it would take forever. The more you fight the less you can hit and the more you need too hit.