How would having more power not be beneficial? He had a sand rasengan that could potentially seal Juubi Jinchuriki.Because why would he need to enter a mode that grants no benefits? Having the other half of Kurama makes Naruto stronger than having bits of chakra from the other tailed beasts, as all he's missing out on is just the elemental FRS. The TSB aren't tied to the Bijuu chakra, so why he didn't use any I don't know.
That was part of my question. He didn't use his TSB either which could have greatly helped his situation.
Hence my point. An explanation is needed. Because if he has RSM then he should still have TSB.