Thresh hook is faster than blitzcranks, the only difference is that thresh has a longer animation (Blitz takes 0.25 seconds and thresh takes 0.5), but the skillshot itself is faster. In case you didn't know as well that thresh's hook is a longer range than blitz's. It is also a 1.5 second stun compared to the 0.5 second stun on blitzcranks and threshs hook displaces the target, dragging them towards him, he also gets 3 seconds off the CD if it hits which is the same as blitz's at rank 1 but by max rank it's a much shorter CD plus the reduction making it a 7 second shorter CD without any CDR and generally you're gonna want max CDR on both. Let's move on to thresh E and blitz E both knock people up but threshes as a larger range and can be used to peel or to pull someone into you.
As for the fact that thresh has to throw himself into the enemy team when he lands a hook... that's kind of the point. It's called an engage. If he hits the ADC, they are now stunned for 1.5 seconds then he jumps on them, ults so now they are trapped or forced to flash, he then flays them into his ult or closer to his team applying a small slow. Anyone who tries to go in to help the adc will hit the wall and be slowed for 99% for 2 seconds which has higher base damage than blitz's ult and also scales off 100% of your AP.
How can you possibly tell me that blitzcrank should be feared more than thresh?