Yeah, i've seen people linking this with FGO as in Musashi got salty that she lost which finally made her reach that shit and beyond in FGO which isn't confirmed, but it would be a nice link to FGO .
As for Iori, yeah, it's honestly one of the interesting aspects about the story . In the bad end, he straight up wants to keep the HG vessel so that he can keep fighting and that's why Takeru fights him . It's cool that in a way, it's a reversal of their roles at the begining since Takeru didn't give a shit about mowing down the city or randos whilst Yori did and as the story goes on, Takeru comes to appreciate peaceful life while for Iori , once he becomes accustomed to constant fighting, it gets harder and harder to ignore his true nature until the end where he doesn't give a crap anymore . He flat out states that the reason he is nice to people is not because he's a good person, but becomes he wants to understand people so that he can cut them down better. It's also why one of the begining quotes is "Iori, you've been born in the wrong age" , which is a pretty great start for a story and i wish they would have done more with it.
As for the Soujorou similarity, Nasu flat out stated in an interview for SR that the more far removed people are from society and accustomed to conflict, the stronger they are while the viceversa applies , at this point it's part of the lore. If you want gains, go train in the mountains.
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4Gamer: Where is the turning point in Fate's history of Japan where people stop being overpowered with their physical living bodies? I remember my "Holy crap, the Genji are strong!" moment in FGO.
Nasu: It's difficult to pinpoint a specific turning point, but the fact is that the strength of the individual is inversely proportional to the progress of civilization. But that's established in our lore as "freaks continue to be born in places that remain strongly arcane". I can see the Edo Period being a point in time when the number of superhumans started decreasing, but it's also an era where people relied only on their human strengths to do things we do nowadays with the help of technology, so I imagine there were still quite a few amazing individuals there.
Sakurai: The Edo postmen and the Ise pilgrims were pretty amazing.
Nasu: Compared to the specs of ordinary men, yes. The toughness of their legs would be considered monstrous by today's standards.
Sakurai: Speaking of legs, at the end of each main story scene, Iori says "I suppose we go back to Asakusa now" and casually walks considerable distances. We see these kinds of depictions all the time in period pieces, and while I know it's fictional, it's still impressive.
Nasu: It's easy to notice the insanity of it when you live in Tokyo (laughs)."
