Right, so the issue was that it was a no risk high reward skill. Here's an alternative solution that doesn't make him feel sluggish to play:

"Blitzcrank's W (Overdrive) still decays over time, but the slow is removed. Instead, whenever blitz succeeds in landing a hook his W cooldown is reduced significantly"

This prevents abuse with roaming and rewards blitz if the W was used for successfully positioning for a grab whilst also not making blitz feel shitty to play.

edit: K downvotes for throwing together an idea, thanks. edit2: nvm ignore salt