That would solve the problem that you would not know what tool you are using, yes. But there is still another: The display what tiles will be affected. Sure, wo know how they work, but not players, that play the event for the first time. Even if there was an extended tutorial explaining it, you would have to remember how they work and if you don't play the game regularly, this can happen very fast.
So even though dragging might not be the best solution for user advancing, it is the easiest to understand.