Duplicate keywords across ad groups - does it actually cost you anything?

Auditing an account with a lot of duplication - the same keyword in the same match type sitting in four different ad groups across two campaigns. Every audit template flags this and I want to be precise about why, because the version I usually hear ("you bid against yourself and drive up your own CPC") is not right. Google picks one and the others do not enter the auction, so there is no self-bidding. What I think the real costs are: 1) You cannot predict which ad serves, so your careful ad copy per ad group is a coin flip. 2) Performance data is split across four rows, so none of them accumulates enough to read. 3) Nobody can maintain it. A negative added in one place does not affect the copies. Those are real but they're not "it costs you money" in the direct way people imply. Am I underselling it?