Actually, telikenetics are usually confined to solid objects with a noticeable amount of mass. This prevents them from moving insubstantial things like fog and air, and in some cases liquids too. On top of that, less power often means less fine control, so even if you can MOVE a grenade at 100 meters (which is unlikely at such a low form of telekinesis, more realistically it'll be around 2-10 meters) you can't necicarilly pull the pin or pull a trigger, or even hold it in the air. The most likely scenario for telekinesis in this RP is gross control in short bursts, such as throwing an object across the room or pulling something towards you. Useful in the right circumstances, but not game breaking.

Also there are abilities that are WAY easier to find loopholes in. Telepathy, for starters.