Imagine this...

You approach a (insert mob name here). You know this monster has three TP attacks: one that buffs itself, one that attacks a single target and one that attacks in an AoE.

Because of this, as you attack the mob, when it starts casting the AoE TP attack, you will instead negate its attack and deal it some damage by using an AoE TP attack of your own.

Let me make that last statement clear: when you have a mob targeted, and the mob uses a specific type of TP attack (AoE, single target or buff), using the same type of TP attack on the mob will not use your TP attack but instead cancel its attack and damage it. Your TP attack literally becomes a different kind of ability when used in that circumstance.

The goal here is simple:
-give combat more depth than "kill the mob faster than it kills you".
-add more strategy to fights by giving you a reason to hold off on using your TP attacks so you can instead use them as counters at the appropriate time.
-encourage parties to have one player at the ready with one of each type of attack for maximum efficiency in grinding.

This could extend beyond simple TP attacks. You could drag the elemental system into it as well, making it so countering an elemental TP attack with its weakness will do far more damage.