Obi may be a talented fighter but he’s not going to be stopping the self proclaimed king of dueling. Luke has a considerable amount of monsters at his disposal and while they may not be the most powerful ones around, they are hard to beat as an army. Obi isn’t prepared to handle monsters and would likely go down to one of the first ones. Their attack range and durability are just too formidable. Luke (Yugioh) wins.
Tomoya is a good guy who knows how to fight when needed but Obi is a trained professional. He will be able to get the win rather easily with or without a weapon. When you have two characters without any special abilities, the trained fighter will win 9 times out of 10. There just isn’t anything Tomoya can do to try and turn the tides of battle. Obi (Snow White) wins.