Honestly in a fight between FSN and Zero the Stay Night Servant basically win all of the same class matchup beside for archer.

Unles Gilles manages to create his monster Medea easily wins.

Medea wins by a landslide

Gilles is carried by his book, his own magic is incredibly weak and he can’t really hold a candle to anybody from the age of gods

Medea is a different beast altogether being one of the strongest mages in history period

Super simp vs minor simp

“Strongest mages in history” is a faaaaaarrrrr stretch but Medea solo’s with her Age of Gods spells.