As far as signature weaknesses go, I think this is one of the milder ones.
When you use it to discard an ally from play, it's essentially an automatically-failed Crypt Chill. If you use it to discard allies from your hand, it's like a milder version of Amnesia. You get to choose which one it is, so you can evaluate where you are in the game and choose the lesser evil.
Leo Anderson's unique abilities means that he should have a few allies in his deck, and that he'll normally be wanting to play one ally per turn at most. So most of the time that you have this card, you should have a choice between discarding allies in play or allies in your hand, so that should give some wiggle room to advoice the worse of the two choices.
If you don't have any allies, it's just a dead draw. That could be a lot worse! However, if you have no allies in play or in hand, then maybe things are not going well already.