You may scoff, but I actually think this is the LEAST that KT could be doing, for promoting their character action game star.
Another Musou appearance is definitely "beneath" Ninja Ryu, but at least he's still doing his best to stay relevant and making current appearances, showing that his company is still interested in marketing him. Musou Stars is just as much an effective marketing vehicle as it is a "celebration" of KT's brands. It likely also means that Ninja Ryu's proper return is likely next up on the docket, as soon as Team Ninja's action game squad is finished with Nioh, and they want to make damn sure people already know or remember who he is. Between keeping him out there and Nioh helping to further shed the "Ninja Dog" image and build up their cred, Team Ninja and Koei Tecmo seems to be already making the right moves to prepare for the immediate future.
Compare that with Capcom's treatment of DMC, at the moment. It's pretty much all quiet on the western front, unless you count 4SE last year, and Dante and Vergil's recent appearances in a 3DS strategy RPG that Capcom had no hand in besides loaning them out. Unless there's another Capcom crossover fighting game coming out soon, how else are they going to help prop up the return of their own star? They're not making this whole thing of "getting Classic Dante back into the public conscious, after nearly a ten year gap since his last game" any easier on themselves.