You're not thinking correctly. The right is not a giant monolith. Many people who lean right or are centrists voted for Biden last election because they too despise Trump. Those are the kind of people who will vote for RFK. Now, they still get to vote against Trump, but don't have to vote for Biden. And yes, of course voting 3rd party is essentially the same as voting for whoever wins up winning, but people are idiots and don't understand that logic.