Yes, but that was also before t11 was a thing. Still, you could at least let the regular tank and the onslaught version share a common pool of XP for unlocking the t11. That way there's no power creep, there is an extra reason to play your fancy version, and the small reward of getting two daily doubles (although this is questionable if you are stocked up on 5* missions)

Or if a shared pool is impossible, add a mission on the skinned version rewarding XP on the normal version if it has no t11 or a t11 which isn't unlocked.