Question about Kha'Zix - Mutating Horror
Last week on a Nexus Night my opponent ambushed with his Kha'Zix - Mutating Horror. His attack trigger went onto the chain, since I only had one unit on the battlefield.
I then reacted to the attack trigger with a Defiant Dance to reduce Kha'Zix might to 2 before his attack trigger resolves und then continuted to react with a Gust, to send Kha back to hand.
My opponent then said that this is not possible, since Kha'Zix gets the pump from his ability immediatly when the attack trigger is put onto the chain. So after my Defiant Dance resolves, Kha'Zix is at 4 and therefore not a legal target for Gust.
I then asked the judge about this and he agreed with my opponent.
But still I do not understand this ruling. Can someone maybe explain the ruling to me? Or were they both wrong?