This is my reply to Do minor modifications to IRV prevent 2PD?
on the other forum.
Without having honed an argument yet, I think that balance is key to preventing 2PD. IRV and FPtP are unbalanced, and Score is balanced.
I offer link
as a balanced modification of IRV. I say it is a modification to IRV because like IRV, it uses multiple rounds within the tally.
Is it a minor modification? No, because the form of the ballot is very different. IRV requires strict ranking (at least, above the sludge at the bottom). The system I describe isn't really a ranking system. It allows a sort of priority list of commands that the voter can provide on the ballot and the tally must execute. Each command can treat two or more candidates equally if the voter so chooses, unlike IRV's ranks above sludge.