Well exactly. The same principle can be applied on mini accounts. Look, if all the top players use him to protect the other 3 champions, there MUST be a reason right? Cuz he's that good at that job if not the best, that's why.
They are not prioritizing Pythion, or Ukko or Duchess or Nekhret or whoever else. No, they put UDK as their automatic 3rd champion.
So at lower levels, it's kinda the same, just scaled down. You put annoying UDK in there, in stoneskin if you have at least a team that can beat normal hydra for 6m. And there you go, your Ronda or whatever else "free" champions are protected to some extent.
Of course at lower levels he's easier to beat, but still he's a pain the butt to deal with when your options are limited.
Even in live arena, i'm in mid silver 2 right now. About 50% of the time i choose UDK, he gets banned. I dont use him all that much cuz he makes things too slow to either win or lose. But sometimes i have no choice and he suddenly puts fear in opponents enough for them to ban him over my nukers or other supports.