is pretty well-balanced, imo, the issue with him is that he's far too versatile a champion, which is why he has had such a consistently high pick rate. He has poke, all-in, crowd control, reach, tankiness and ally utility all in one kit, and so has more raw tools than most other supports at all stages of the game, along with few pronounced weaknesses.
If I wanted to streamline Thresh, here's how I'd do it:
- Make him melee, and reduce his range to 200 (his range doesn't contribute to his primary lockdown power, imo). Maybe buff his base movement speed a little.
- Remove the passive on his E, as you mentioned, and seriously buff his base AD and growth in compensation (him being melee would allow him to continue proccing
without a problem). Also, remove the attack wind-up reduction on Thresh's basic attacks.
- Buff his base armor and give him scaling armor and MR per level. Also perhaps buff the armor and AP given by each soul.
- Make Death Sentence's stun/pull scale with level (from 1.2 to 2 seconds, for example). Perhaps reduce its base cooldown at all ranks and remove the cooldown refund on successful hit as well.
- Remove the single-target restriction on Dark Passage, and have the shield last as long as the lantern (so 6 seconds or until pulled). Perhaps also increase its base value and/or AP scaling.
- Reduce Flay's cooldown per rank, and perhaps increase its base damage and/or AP scaling. Also, maybe remove the slow, but instead increase the ability's displacement, so Thresh would have a much easier time repositioning targets.
- Remove the multi-target restrictions on The Box (i.e. having it deal no damage past the first wall and slow for less time), and perhaps reduce its cooldown, either per rank or at all ranks.
The way I see it, Thresh's defining characteristic is his ability to engineer all-ins for his team, imprisoning single targets for his team to finish off and bringing in allies with his lantern. Secondarily, I feel he can also afford to have decent damage and save potential, but he also needs to have defining weaknesses. Imo, that weakness should be a lack of reach (Thresh should only be able to affect targets he's caught with one of his abilities first), constant exposure to the enemy, and windows of extreme weakness in-between his powerful abilities. His range and E passive go against all this, and I think making him melee and balancing his abilities accordingly would be a major step towards making him a more specific pick. Thresh is a tanky support in any case, so I don't think that would harm him, but as long as he can be a tank support and a poke support at the same time (plus a utility/sustain support with
, to some degree), he's going to keep on crowding out a lot of other potentially interesting picks.