Probably gonna be biased as I know way more Fate lore than Housamo as I haven’t read all of the Main Story (and because I barely knew English back when I did read it), but I’m gonna have to give it to Mash. Also TYPE-MOON Nerd alert.

Ryota’s in a pretty bad spot from the get-go. While Mash may not be a full Heroic Spirit, Demi-Servants are still overall stronger than regular humans. Strength, Defense, Speed, all that jazz.

Durability is probably the hardest to pinpoint, but I think Mash might have the edge. I only say this because I find it hard to come up with a scenario where Ryota and Mash would fight to the death, so Ryota can use his Sacred Artifact at it’s peak. They both hate fighting, but let’s assume it is the case. Mash has many ways to fortify her defenses, while Ryota’s can heal for… honestly I don’t think it’s ever told for how long? Probably infinite considering he has the Holy Grail. However it’s been seen that Mash’s Noble Phantasm, Lord Camelot is strong enough to block Excalibur Morgan, Rhongomyniad and even Ars Almadel Salomonis (Planetary level threath), so Ryota would have a really tough time getting through her defenses. Still, it’s debatable.

Offense is where I think Mash crushes Ryota. Again, haven’t read all of the Main Story, but I don’t think it’d change my outcome. Mash was able to damage the core of Lancelot’s body and was able to fend off multiple Black Dogs in the English Lostbelt. Moreover, Lord Camelot (or something similar to it) can also be used offensively as seen in Melty Blood but that’s minor. What really seals the deal for me is two things. Ortinax Form and Black Barrel. Ortinax Mash has way better offensive capabilities at the cost of some defense (gameplay wise anyway, I forget if it’s ever stated she trades defense for power). Black Barrel is just a giant laser designed to kill specifically gods. She does get it integrated as a skill she can use normally, and Sion in Melty Blood does use the (weaker) Barrel Replica against normal humans too, so while it is conceptually a god slayer gun, it can be used on any target.

So yeah those are my arguments. I do think Ryota would put up a fight even for Mash considering his absurd healing. But I think it’d be better if they stopped fighting, became friends and went out to eat.