How a 20-inch-gunned Hood could break treaty negotiations

What would a successful 20-inch-gunned Hood do to naval treaty negotiations?

It could make agreement nearly impossible unless Hood received an exemption or every power was permitted a comparable 20-inch ship.

A 20-inch-gunned Hood would threaten the logic of interwar naval arms control. Britain would be unlikely to surrender such an expensive and singular advantage merely to make an agreement easier. Negotiators would have to write a special rule that preserved Hood or establish limits under which every major navy could pursue a 20-inch ship. Either choice would make the treaty harder to sell and could push the naval race toward much larger weapons.