Just because people are often bad at Blitz/Thresh doesn't make em balanced.
This seems to be the common defense for them. Hey insert random insult, just insert basic anti-grab tactic and you win the lane/game easy. Players who main one of these guys know the basic anti-grab stuff you can do, and play around it. When it's all about the zoning, they are overpowering champions who exert an unreasonable amount of threat range to the lane.
If they didn't pick sup before your team(or if its normals), you can't counter-pick them. If they are smart with grab positioning and timing, you won't be hiding behind minions or juking the grab without running into threat range of something else you don't want to get hit by. If they don't throw them at bad times, allies won't be able to jump in the way.
The design values blog said it best really: "A fight loses its excitement if the first punch wins – it's what you can do after that adds depth and complexity"
is balanced because his presence AFTER the grab is much weaker. The entirety of his power is loaded in to his Rocket Grab. His other skills aren't bad, but they are comparatively very low impact skills.
however... what a fucking mess. He gets the incredibly high impact grab skill on a lower CD that gets even lower when hit. He doesn't have to commit to jumping in either. Blitz can't stop himself from pulling if he accidentally hits the wrong target. His W is an incredible utility skill that's basically an ultimate in how much power it brings. His E not only gets the knockup of Blitz E, but it has displacement, a slow, AND bonus auto damage for a RANGED ATTACK. And of course, his ult is bonkers good at teamfight control. Blitz just gets to sit there putting out maybe 300 damage a fight.