I think this is a meaningless stat
if you think about it, pure duelers who started from lvl10 dueling are going to always have a lower avg duel XP per win. this is because, in the early levels, it is VERY HARD to even find a person to challenge worth more then 100XP because of how duel XP is calculated (if I am duel lvl 20, and I challenge a duel lvl35 player, how much XP do I get? not much). then, if you do find higher level players to challenge who are worth more then 100XP, the problem is at lower levels there is the disparity between power of duel weapons.
a dueler who begins at say Level 50 XP will have a much easier time maintaining a high duel XP per win average. The disparity between weapon strength for a lvl50 vs a lvl65 does not overwhelm the chance fror the lower level player to win. however, a lvl20 using a boomerang versus a lvl35 using a derringer (or comparable melee weapons) makes it too difficult for the lower level player, whereas a lvl50 using a revolver versus a lvl65 using a peacemaker is not as much of a 'gap' in weapon strength.
and then there are the zero motivation duelers; a stretch of zero motivation dueling to rustle up some $$ will absolutely tank a players avg duel XP per win.
and what about about players who attack you? what if some low-level dueler wants to make his claim to fame by beating you and keeps taking shots at you? that will tank the avg duel xp per win as well...