The kusunagi is also a physical sword, whereas totsuka is a spiritual, ethereal blade. Totsuka is basically unstopable until proven otherwise, seeing as how there are only 2 spirit weapons in existence, both of which not even the Sage possessed.
1. He would still seal himself so he can only use it once
2. He has infinite chakra, not unlimited, so he can still only seal up to 1/2 of kurama at most.
I theorize that he gave sasuke his Totsuka and Yata mirror. There were little to no feats from these spiritual weapons with 0 back story, and they would be immensely useful in this fight.