The build looks pretty bad for late game/team fights. Once you have 70~ souls you want to focus your build around the minimum damage from your flay passive, not the amount you get from a full wind-up because this is useless in drawn-out combat. Wit's End is very good on Thresh but I would get BotRK instead of Bloodthirster, and some more tanky items like Spirit Visage and Warmog's.

Triforce is also not optimal on him, since he has one of the lowest base ADs in the game. If you need more mobility then Zephyr or Talisman of Ascension would be better imo, or just take movespeed quints.

Also, armor pen is extremely inefficient on him because most of his damage comes from his flay passive. You should either take hybrid pen or magic pen runes.