Thresh actually isn't a bug. He's a ranged champion with a weapon that people look at and think should be melee. There's a clarity issue between his visuals/animation (melee) and his game mechanics (ranged).
Blitz's hook is just the most visible way to see the behavior, but it has been declared as intended. It happens with any form of CC, from flame chompers to Morgana bindings. It probably even works with the newest CC, Grounded, but I haven't tested that. It has to do with the order when the abilities are cast. Ezreal sits in place for a moment before moving, but he's already used the ability and it will go through if it was able to when he hit the button. The CC hits while he's sitting there (and in Blitz's case, the pull follows immediately afterwards) then Ezreal Moves.
Using multiple words for the exact same type of CC is a clarity issue. Entangle is different from Ensnare, so shouldn't Bind be different than Root? The fan made and maintained Wiki has actually done a lot to reduce the confusion, but the in game text still uses at least 3 words for the exact same type of CC.
Ezreal's Q acting the way it does might be for game balance, but Clarity demands it be documented better. We've got abilities that apply spell effects, apply on hit effects, apply both, and apply neither in the game. Having an ability specify what it will apply is something that should probably be standardized across the board.