If you encounter around to balance, to avoid the impact of the damage and status effects indefinitely, that means that every encounter will be a kite-fest and you do not even need melee DPS; ranged classes(tera gold) will be far superior. But you say that mobs need to be kept in one spot for the damage dealers to shine. Right. If you need to keep a mob in one spot, you will need a character taunting and soaking up damage, you will need the character to be cured.
Tanks of Tera are only good in PvP because of their health pools (maintained by healers) and defenses (buffed by healers) and healers are good because they can heal themselves and others. If they also do good damage, they're way OP, and if they're OP, they are not easily replaced by mere damage dealers, and guess what. You don't need damage dealers.
It's an MMO. If you make encounters too easy or boring, PvE players will lose interest, and take their subscription money with them. If you have tanks and treatment requirements, you might as well make this single-player game and balance everything for solo players, with multiplayer thrown in as an afterthought.