If Thresh doesn't need any changes why does he...
have this passive
Basic Attacks: Thresh's basic attacks do not utilize projectiles, and his basic attack wind-up is only reduced by 0.25% per 1% bonus attack speed, rather than the standard 1%.
to balance out this passive:
Passive: Thresh's basic attacks deal bonus magic damage, increased with the time he spent since his last basic attack. Bonus Magic Damage: Souls + up to 80 / 110 / 140 / 170 / 200% AD
Kinda stupid that they needed to give him a negative passive just to allow him to have powerful poke with his AA. Without the above he is a broken as hell ADC.
Honestly, he doesn't need these passives. Take them off. Give him compensation with more power elsewhere in his kit I don't care, but this is just sloppy. He should not need a passive to balance out giving him a powerful AA poke that allows a ranged champion to buy Relic Shield.
EDIT: I actually really want to know why he needs this and not more power in his shield/ability base damage/or CC? not really saying he is OP or whatever, I main support and I don't have a lot of problems with him. I just want to know why he needs this.