Who is Yasuke in Assassin's Creed Shadows?
I'm a game designer who studied history in school. My focus was Mediterranian/Roman studies and Japanese history. We learned how unreliable our information is and historians need to posit theories based on historical clues. The Azuchi–Momoyama period was filled with strife because of Nogunaba and the classification for what makes someone a samurai was not as rigid as it became in the Edo period. If Yasuke was still around in the Edo period, he would have officially been a class of samurai, meaning he was effectively a samurai under Nogunaba's employ.
The gaps in that history make room for Assassin's Creed to tell their own fictional story. Their games have never been historically accurate. Leonardo da Vinci didn't build a tank for an assassin or anything remotely similar. I haven't enjoyed the past couple AC games but I don't think including Yasuke will be the reason this game doesn't live up to expectations.