Seriously, why is Thresh's Q allowed to be fundamentally different from every other skillshot?

The direction of the windup is whatever he was facing when cast. That is completely independent of the projectile direction. He can literally be going in one direction and hook in that direction, only to send the Q flying in the exact opposite direction.

I'm all for mind games, but the cast animation is false information. To illustrate the problem, here is a more extreme example:

Let's say Leblanc get an update for her passive. You can now control it like a second unit; you can move it and make it cast spells in addition to autos. The tradeoff is that it still doesn't deal damage and it's E doesn't root.

Situation: An enemy Leblanc W's over the wall. You have no idea if she's real or not. It manages to hit E on you. Do you flash to break the chain? "But you just check her items!" Nah, this now get changed. There is now no way to tell which is real and which is fake other than trying to look at patterns of movement over a period of time (the real one will most likely be more guarded).

This is the same kind of problem with Thresh's Q cast. At the very least, it gives you no information other than it's being cast. If you don't know that Thresh's Q behaves differently from pretty much every other skillshot in the game, then this is false information.