He inflicts 2 debuffs with each of his attacks. Also I'm not sure, but potentially tm reduction may also be considered a debuff, again I'm not sure how that works.
Anyway, that's 20-30% tm for him assuming all debuffs take and another 10-15% for the entire team.
These are huge difference makers, especially when you're determining who goes first. It will give you extra turns here and there which will be the difference in battle.
With that said, it's a solid zeta on the most OP character in the game which means it's going to be useful in many different teams and for a long time.
Best zeta in the game, IMO is raid han's shoot first. It makes him one of the best characters in the game.