Well this doesn't sound like CT's fault necessarily then.
First of all I'm really biased against the balance team because I'm convinced they do not talk to Design team members and balance everything the wrong way (for example not touching Yasuo's damage but nerfing his Utilities, literally his defining features at the time). A champion taking a long time to balance is a failure of the balance team.
And if we're comparing really old designs to Thresh on the basis that he brings a lot of new to the table, what do we say to modern post-Thresh Supports like Braum, Rakan, and hell Pyke. Would we hate them just as much for the same reasons? Or what if Thresh never broke the mold and we never get interesting designs like the ones I mentioned and we just get more Jannas.
Also for the generalist comment, remember over this same period of time Lee Sin, Elise, and Evelynn/Vi were dominating the jungle despite being generalists. Again, I see this as a mark against the balance team than CT and Thresh, as well as Lee Sin and Elise and Vi's designers in particular ('old' Eve is more debatable in my eyes)
Design and balance are two totally different issues by the way. I can see where you're coming from with the Balance arguments, but I really don't respect the Balance team's decisions and have played through a lot of their philosophies. However, I don't think the design argument that he stands out compared to other Supports in his release is a very valid one. Hell I know I've seen posts and videos praising Thresh for breaking ground and enabling more interesting playmaking Support designs. At best I can accept the generalist problem as a problem, but that can be handled with good balance decisions.