Pentaban? Nah. Way overkill. The only one I agree definitely needs some sort of fix is Blitz's insane early-game superiority due to the fixed speed of his Rocket Fist, which is especially problematic when everyone's using base movement speed. Some champions that are especially slow often have a really hard time against him due to the speed of that fist, as well as the lack of casting time.
His pulling+bursting ability on a bottom lane is almost guaranteed death for whoever gets caught by it, and that fist of his moves in fast. Maybe a little too fast. At least Thresh has kind of a wind-up first so you can see it coming, Blitz's has little to no casting time, and he can follow it up instantly with a big stun while any carry finishes off what he started. Players that can target it well are nightmarish no matter how quick you might be at dodging it.
He's not terrible mid or late game unless he's been fed beyond reason, but early game, especially when no one has movement speed boosts, he's too effective.
Maybe scale the speed of his rocket fist a little to make early game a little more fair, until people have more reliable ways of dodging it.