So literally any well composed rainbow at all.
Well composed because if the oracle card doesn't work with the rainbow, its not put together well. And if it doesn't have x2 Dex and the deck is in gold league, it sucks by definition except in very niche cases.
I'm sorry, but I can't really agree to an outright ban on all rainbows. They're mean and can be hard to deal with, but they aren't even the most powerful deck type. See: Death Stall
And the way you defined "Oraclebow", its literally impossible to put together a mono-rainbow deck without it being this. Give me a mono-rainbow deck that is otherwise if you disagree with this point. If you were saying put a ban on those "30 card insert your oracle card skeletons for easy arena deck" that saps creativity out of the process, I could agree with that more. But I can't agree with a ban on rainbows.
Mono-rainbow is a term for a deck that is fully rainbow, as opposed to a half rainbow half water deck, or a half entropy half rainbow deck.