I feel an attack that draws all aggression from enemies is very strong
Unfortunately our feelings are often very misleading when it comes to game balance. The only way to find out if our feelings are warranted or not is to collect some data through playtesting. So I would recommend you to implement that feature in a provisoric way, try it in different scenarios and see what happens. Possible results could be:
- It is completely overpowered because it allows the player to draw all enemy damage output on one party member which can then be made almost immune to that damage.
- It makes almost no difference. Maybe the player already got enough tools at their disposal to control what units the other side can and can not attack. Maybe it isn't even that relevant in your game which character in particular tanks the enemy attacks.
- It is almost always a mistake to use that ability, because no player-unit is capable of surviving a turn where the whole enemy team focuses their damage output on them.
But the only way to find out is through playtesting.
OK, so what if we find out that your intuition was correct and the ability is indeed overpowered? What can we do about that?
We could limit its use. Add a cooldown so the player can only use it every other turn. Or we could make it only usable a limited number of times per-combat or per-dungeon. Or we could have it consume some resource which is hard to replenish.
Or we could introduce a counter to it. Some enemies might be able to ignore it. Some enemies might even hit extra hard when they are taunted. Some enemies might be able to negate the taunting-state of the character so the other enemies can attack normally. That way the player might be able to win some battles using the taunt strategy, but has to find a different strategy in those battles where a counter is present.
I am looking forward to playing your game.