(Fate fan since 2021 here, got into it a lot and also a bit of everything from Garden to Tsukihime but mainly Fate so maybe I'm gonna be wrong with what I'm gonna say)
Nasu did say something about Ryougi, namely that while the MEoD can destroy pretty much anything by cutting their lines of death, you have to actually land a hit to cut that line. MEoD can't just cut stuff from afar, they would get close and land a hit. And the problem is that Servants are so above even augmented humans and mages the difference in their physical parameters makes it nearly impossible to engage them head-on (that plus the Servants are basically projections from the record of the Throne of Heroes so to really destroy the Servant, you'd have to destroy the record itself). And I'm not even talking about the broken ones like Gilgamesh, Karna, Saber, Achilles, Sigurd, etc, technically even a shitty Servant like Shakespeare would shred both Shikis to pieces with his bare hands. It's also kind of the idea behind Shiki Ryougi as an Assassin in FGO, she's a weak Servant E-rank strength but has powerful skills.
Essentially, the idea is that on a technical level, MEoD users can kill Servants but they'd normally lose in a fight due to the Servants being so absurdly above human limitations even going after some of the weakest like True Assassin would be like a mouse fighting an airplane.
Also found something from a Q&A Nasu did but I don't know how old it is (source, Type-Moon wiki, Shiki Tohno page, abilities section)
Q: In the other Type-Moon works, who else besides Arc can fight against Servants?
A: If we're working on the condition of one on one, with an extremely average Noble Phantasm. Generally most of the 27 Ancestors, Kishima Kouma, Aozaki Aoko.
If it's just a defensive fight, but would still be a fight, then Ciel. Shiki (Rakkyo), Shiki (Tsukihime) are no match for Servants....but Ryougi Shiki (3rd personality) might be able to go as far as the Ciel class.
Again, I don't know how old this statement is and it's still working, especially after the Tsukihime remake