will never be strictly competitive even if it were cost-free to run because p2pool will always have a higher orphan rate vs. well-run centralized pools
Except that, in practice, it has a lower empirical orphan rate. The design currently has a communications advantage.
Which is why I said "well-run" and went on to talk about how the design advantage that p2pool currently has by forwarding txids rather than transactions won't last forever.