Yes because they are fair to play against. Blitz does nothing if he misses his hook, while Thresh still provides get out of jail free cards via his Lantern and zone denial via his ult. If you dodge blitz's hook that is your cue to jump on him/adc because at that point they have little to nothing they can do but run away.
This gets into the main problem and why Thresh and Tahm Kench are toxic by design. They are champs that by design don't lose because not only are they lacking real weaknesses but they also cover for the weaknesses and misplays of their teams so well. Let's take an example of Thresh "losing" to better explain why I take issue with him as a support.
Say Thresh/Cait are going against a Jinx/Soraka. Thresh hooks Soraka but Cait attacks Jinx allowing Raka to spam heal Jinx and win the trade with ease.
Sounds like a case of "oh Thresh/Cait got out played" but the problem is did they really? What play did Soraka/Jinx make that resulted in them out playing Thresh/Cait? The answer is simple, they didn't. It wasn't that Jinx/Raka out played Thresh/Cait it's that Thresh/Cait misplayed the lane. That is the inherent problem, Thresh is able to make plays, while Raka being successful is entirely dependent on her enemies screwing up. This is inherent to a number of supports, especially the non-tanky supports like Sona/Raka/Janna who either through nerfs or reworks have been hit so much that they no longer make plays, instead they simply exploit mistakes.
Exploiting mistakes in and of itself isn't bad, in fact all champs should be able to do so, but when a champ ONLY exploits mistakes because they lack the urgency in their design to do anything else you have a problem. This is compounded by champions like Thresh/Tahm who have all the urgency, they have all the control and all they have to do is not screw up in order to be successful. I would rather play against champions who reward me for out playing them than play against champs that force me to depend on the mistakes of my opponents.