Like u said that Irene was reverted from the dragon form by Wendy ,why did not Ezra win at the start. Because Wendy enchanted Ezra at the start . so, if Wendy is really key of winning ,they both had to win at start so what Wendy did is just revert Ezra nagama power that can destroy the greater...
What Wendy do is just revert Ezra power become dragon slayer magic not boost up so what's Ezra use to slash Irene out of dragon form is her nagama power is reverted to be dragon's element by Wendy and in manga said many times that she is third strongest individual