check your achievement tab to confirm ingame, you only need to kill 1 version for it/no need to swap (or even be on Ultimate)
*you also can’t change Ravager version on that char on that playthrough “vanilla”, you need to “hack” your Ravager token to swap versions with ex console commands via ex tqFans tool [Tool] GD Console Unlocker - change Ravager, reset Mogdrogen, teleport / warp if stuck etc. in Main Campaign
or you need to do the quest again on a different char/difficulty (will give different tier Helmet depending on difficulty tho, so you wont get the legend version from different ravagers on the same char without the console “hack”)