In A Land Of Myth

Merlin: I’ll do it!

I have to recalculate because canon Leon ≠ fanon Leon.

Canon Leon is serious in fights but silly outside of it. He's a good fighter but blames his failures on 'letting Arthur win'. Honourable idiot. He's quick with a sword and a good strategist but not quick witted, if you catch the difference. He's a long trained fighter since he was a child and practices daily while also training youngsters. This means loads of easy wins outside of (rare) serious battles.

Elyan on the other hand was born and raised a blacksmith. He's likely more brutish with the sword because of it but also stronger and more creative (because you need creativity to work with iron). He also left home early and fought himself through life, which means he likely has better people skills and is accustomed to different kinds of fighters. He would also be more reckless.

It really depends. Technically, they would be evenly matched. If Leon prepares beforehand, he would use Elyan's recklessness to his advantage. In a sudden fight, Elyan would likely have the upper hand because he's more mentally flexible. Leon is more of a leading figure due to his experience as a knight and Elyan dies while Leon doesn't.

In a fair fight, I would guess Elyan to fight fast and lose his energy first. Leon would last longer, if he manages to stay upright through the first attacks.

stars @merthurmicrofic