When you dule in a practice arena , you are practicing your skills. More people use the practice arena making it the better one. I think you should get 10-30 gold , a treasure card , or a house item for winning. Right now you win nothing for dueling.
Sure you do! You win plenty of stuff for dueling! Oh, wait. You were talking about PVP? Yeah, that's not dueling. That's PVP, there's a difference.
Dueling is going outside the arena and actually battling monsters and such to earn your rewards.
Practice PVP is, in essence, a Legendary being paired against a Novice, the novice gets owned in one blow. The Novice starts crying. The Legendary gets reported.
Is that worthy of a reward?
If you really want rewards in PVP, try the actual RANKED battles. You get scraps of paper that you can give to Diego, which he will exchange for clothing that is near-impossible to use outside of the arena.
On the flipside, he has some pretty cool pets to trade, so there's that...