Mu don't even have breakthrough in China yet.

Thats a pretty decent lineup. Can't really think of somehow making it better. Mu isn't used that much late game because there are similar ninjas with better skillsets but there's nothing stopping you from using him.

What are the similar ninja with better skill sets?

Well, if you're using him for his mystery and cc on chase, both Kurama and 6PN are better replacement since they hit more targets, and can fire off mystery every round, not every 2 rounds. His clone and revival passive aren't really very important late game. Edo Hashirama is also a possible replacement for Mu, since his mystery is undodgeable, hits 12 units, and his chase both immobilized and steal all chakras. All 3 of them requires serious saving, either cps or ss, but that's why they are late game ninjas.

I'm actually literally 1 or 2 10 pulls from my gnw sr, I'm crossing my fingers for kcm naruto. I do feel like mu can be good pos 1 or maybe as a more supportive role in pos 2. I just needa find the right team.