Well... without master their Mana Supply will slowly Deplete ..True...But Under Certain Special Circumstances they form contract directly with the Will of the Planet...Which gives them the title of Grand Servant...Or a Counter Guardian..and they receive Mana directly from the Grail or rather the Will of the Planet

So.... Kirito would win. Lol.

Kirito loses.... Excalibur is way too powerful..

He also has Excalibur. Booooom! Lol. But for now we’ll just have to agree to disagree about who would win.

Hhhhmmm i would possibly say saber but kirito has been training with swords for a long time

Saber has been training ever since she was 10 years old

But Kirito has had to fight all sorts of monsters with all sorts of abilities that pushed his skill why passed hers. Plus she has had a kingdom fight with her and Kirito fight solo for a long time. Lol