@Derp Given the whole theme of my whole "Are MUs a tabletop game with writing or creative writing with some minor rpg elements?" thing, I think this applies to my answer.
In tabletop RPGs, EVERYONE in the game gets XP at the same rate, same time. You play maybe 1-4 times per week maximum, so as a GM and player you give/gain xp as a group as you go. XP growth speed is a common topic in tabletop RPGs, as is the concept of gaining experience itself. XP/sheets is 100% a "tabletop RPG" element.
However, in terms of MUs, everyone is on at different times. Some people are on ALLLLL of the fuckin time. So you could have 2 players join at the same time but "PlayerA" may have a day job and 3 nights a week availability, "PlayerB" has no day job or need for sleep and is hound-dogging XP for everything, and the next time PlayerA and PlayerB meet...they look like the Rock and Kevin Hart standing next to each other. What the "mega xp asap" players in tabletop RPGs often don't understand is that there IS something detrimental to rushing to fill out all the dots on that character sheet.
Because of this, I 100% believe that MUs should be capping xp expenditures to a maximum weekly spend. You can't punish active players for being active, but you CAN try to ensure that "ultra-active" players don't use that as a way to eclipse the rest of the game in terms of sheet capability.
I think FS3 (@faraday ) handled this very well. Even with the biggest difference in stats, it was still ultimately Fudge so having better stats may have gained you extra dice, but didn't ensure godlike capability over your peers.
- Limit weekly sheet changes to a maximum cap
- Focus on trying to ensure the game has a sort of "capability range" in plots so that newer characters aren't always being eclipsed by older characters and older characters aren't being slowed too much by newer ones
- Understand that existing RPG systems (World of Darkness, D&D, Star Wars) are "level-based" in terms of how filled out the character sheets are, and that some players will ALWAYS rush to get xp/min max
And most importantly
- If you don't want your game having an XP imbalance (or if +rolls aren't that important) then either ensure your MU doesn't have an existing RPG system as a base, uses a more free-form type system, or maybe even no XP system at all