Cast time on Threshs Q
 

Way too long. Blitzcranks grab is an instawin ability that instantly pulls the enemy and it doesnt have such a long cast animation... I think it should be lowered or, like Blitzcranks, the cast should be instant.

On another note, it would be interesting to see what would happen if Blitz could leap at his target with the second cast XD

This ^. You're forgetting the most important thing about Thresh's Q. It's not meant to necessarily pull them to him. It's more for pulling him to them or slowing them from catching a friendly/getting away. Blitz's grab is all about completely removing someone from a fight. They're two completely different mechanics.

Also note that the pull lasts 1.5 seconds. Completely suppressing the enemy for the duration. Its basically a 1.5 second stun that can also relocate the enemy, AND allows you a gap closer. There's also the added functionality that you can jump through walls with it, onto minions or for ganking a lane.

It's far more in depth than Blitz' grab.

No matter what hitting Tresh's Q requires the enemy to disconnect or to be stunned/snaired already. You need a lot of luck to land it and dont start talking about high skillcap. You can't land it on a player who is able to move.

The same could technically be said about Blitz's grab. A good player can easily avoid a blitz grab the same way a good player can easily avoid a Thresh grab.

It isn't Blitz's grab, it has other additional uses other than bringing an enemy to your location.

It's stronger than blitz's grab, so I like that the wind-up is there. If it weren't, well what use would blitz be anymore?

Seeing as Thresh's Q has a longer windup and (what it feels like) slower travel speed I have to disagree. It's simply not true that both are equally easy to dodge.

It really is true. Also, Blitz grab doesn't quite have the utility that Thresh's does. If Blitz accidentally grabs Rammus he can't just cancel the pull.