We're are comparing defense capabilities of BSM avatar and senjutsu V3 susanoo. Naruto maintaining SM doesnt relate to anything here.Lel tittle is wrong Op, instead of bsm there should be bm.
BM = legged v3 senjutsu susano. Reason: Juubito's attack made Sasuke lost sussano completly while Naruto only lost chakra kurama avatar preserving sage mode. Yes, after Obito's atack Naruto stood up right away with sage mode on.
This proves BSM > BM