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In my opinion, if something is turned on in 1 policy, it should reflect that in some way in the other policy catalogs so you know when you go to set it that it was set already. It shouldn't prevent you from setting it, but should warn you.
My question is more about what happens on the endpoint. When we have two Intune policies that manage the same setting, and in one policy that setting is enabled, and in the other policy that setting is disabled, it's our unstinting that on the endpoint when policy process that setting will not be managed at all. If this were two GPOs, we would see the last policy in the link order would win. In Intune, neither policy wins.