There is more then enough that is different that they all can co-exist.
Maybe they could coexist even if they were hardly different at all.
They are still nearly identical in terms of their role filling a software gap. Remember, people don't see or know what the differences are until they actually play the game. Until then, it's two open world samurai games with sword combat. And a lot of people may choose only one such game per year, not two. Or pick one and get the other later on discount.
I thought it was crazy that after so much time, TMNT Cowabunga Collection released shortly after Shredder's Revenge. Both of these titles are very different, certainly enough to "coexist", but they only really needed one side scrolling classic style TMNT game in one year. One is surely taking sales from the other and vice versa.
Just because they can coexist doesn't mean they won't fill a similar role in the market and affect each others sales to some degree.
To a Western audience, there's hardly a difference between the setting being Japan and China, Samurai or Ninjas, 1200s vs 1800s. The game is about being in pre-tech Asia with a sword. I don't think there will be a "problem" like one of the games will fail vs the other as a direct result, but it's a legit point to make that these titles will be taking a bit of each others' thunder away.
It's like two similar big games coming out to complete on PS and XB, only Xbox never made theirs so there's two on PS instead lol.