I'm not sure where you're getting that. If it's incompletely burned in the preburner, it gets completely burned in the combustion chamber. And even if that we

I'm not sure where you're getting that. If it's incompletely burned in the preburner, it gets completely burned in the combustion chamber. And even if that were true that combustion happening in the preburner was wasted, then full-flow staged combustion would be equally bad because it still has preburners.