I agree that it isn’t diminished. The intrinsic value of his achievement is what it is.
If he were definitively found to have once been a slave, though, it adds to his accomplishment. That one could rise from the lowest echelons of a society and still make a permanent mark on history is a laudable achievement in and of itself, separate from but intertwined with his becoming a samurai.
Think of it this way: representation matters. There’s all kinds of studies that show this. Seeing others who have overcome the same or similar obstacles in life matters- it gives you hope that you can do likewise. And the sad truth is that slavery still exists today, worldwide, across religious and ethnic demographics. It’s just not “open and notorious.”
A less incendiary example: there’s lots of great guitarists in music history, and Django Reinhardt is one of them. His contributions to jazz, gypsy jazz, bebop and traditional Romani music are epic in scope, and would be sufficient to immortalize him. But he did what he did with a damaged fingering hand- only the index and middle functioned after his hand was damaged in a fire. He merely invented new techniques to circumvent his injuries.
Decades later, though, his story of finding a way to play guitar despite a terrible injury inspired Tony Iommi to keep playing and rethink his techniques and gear after he was injured, losing some fingertips at work, just as Black Sabbath were starting to get major attention. The history of metal and other entertainment would have been different had he given up.
And he didn’t give up because a Belgian jazz guitarist didn’t either.
