If the Uchihas use Susanoo, Muu can go invisible and drift behind Sasuke and Itachi. Then Minato teleports to Muu, warps away Susanoo, and either Minato kills them with a rasengan or Muu kills them with an invisible sword attack. Muu can split bodies, and Minato can use clones, making this strategy much more difficulty to counter with increased numbers.
Then there's the fact that Minato can warp jinton towards either Sasuke or Itachi using Space-Time Barrier, or teleport Muu into a convenient location right as he's about to execute jinton. Neither Susanoo can tank jinton.
If Kirin somehow gets set up, Muu can destroy the rain clouds with jinton.