Okay. I think I know one way EMIYA could beat Scathach without facing her directly.
He' a Counter Guardian right? Why doesn't he just goes back in time and kill Scathach while she was a kid, thus still mortal! Though EMIYA's track record of doing that to his past self isn't great, theorically he should be able to do this, right? Though the weapon triangle might screw him over too, even if she's still a kid if we're looking at Kogil and Gilgamesh too.
*Joking, but I'm also curious if he can even do that, alternate universes be damned.*