I've always preached he's broken since his release. Like, he gets so much cc, damage, utility and stats for free from his kit.
Passive grants him free armor and ability power over the duration of the game, and while you usually have to be near the souls or lantern them to get it, I've seen many times where the souls just magically travel to Thresh without him being near them. Absolutely bogus passive that grants an abundance of stats,
Death Sentence stuns you for 1.5 seconds, has a large range, and if it connects, the cooldown is reduced by 3 seconds. An amazing, powerful ability rewards the player when landing the hook is rewarding enough. It can serve as a gap closer, or as an escape, as well as compliment the rest of his kit flawlessly. Not only that, but the hitbox is very inaccurate. It's thicker than it should be, and often times, I see it snake in between huddling minions miraculously and connecting to champions. The wind-up never gives you a hint as to where he'll toss it either, as he only changes facing direction AFTER he throws the hook instead of winding up.
Lantern provides a free flash, to either close the gap or provide an ally with an escape while also providing a shield and granting vision on top of collecting souls for his passive.
Flay knocks enemies up, although for a short time, damages, slows, and grants Thresh a passive of strong auto attacks based on how many souls he has collected as well as time in between his auto attacks.
Then, there's his ult... 99% slow first break, pretty high damage for a support especially considering the free ap he gets, and slows everyone else for nearly 50% and lasts a good 5 seconds.
His kit is extremely overloaded. When I look at Bard, I think to myself... why should Death Sentence, Flay and Pandora's Box do damage? Isn't the passive on Flay good enough? He already gets a good amount of armor and ap over the course of the game. It'd be more tolerant of him if he was just this high utility, high cc machine slightly tanky support. Instead, he's this high utility, high damage, high cc machine that functions as a tank.