Sanji never fainted. Don't headcannon that as he was on the ground, but he wasn't defeated if you got back up to fighting and he did fought them both given his talk is about fighting them both, not that he didn't. Your in denial on your headcannon there.
Lmao
Sanji had his ass on the ground besides marco, they were 2v2.
It's a matter of teamwork, like the rooftop, when the SN weren't teaming up they were easily brushed aside, but when they had a collaborative plan they almost killed big mom.
Sanji and marco had no teamwork and they were doing individual attacks that has no effect.
You can even say that both marco and sanji were fighting 1v2 but they were easily dealt with.