Duelling is supposed to be fun. I love duelling with stronger people, even though i'm always 99% sure i'll loose to them.
If you had this "loose xp when loose duel", it will be a great loss. Not only weak players won't come to practice and get better, but the best ones won't even find anyone to compete with them.
For a constant gain, i'll probably just say no. Why would you get xp for just standing still waiting to find another duellist ? And since there's never any new round, you get the max ticks. In 10min and 10sec, you get 10 ticks, whereas in battles, if a round ends in 3min and 58sec, you only get 3ticks. So basically 7-8 ticks in 10min and 10sec.
Thirdly, don't make every server a grind server.
Finally, it will be a leecher server if such an option was implemented, people going afk after 1 duel, coming back in 2min, then duelling once, etc...