I personally find XP in 2e to be pretty easy for the DM: just look up the monster. It doesn't have any of that fiddly base + HP multiplier business that 1e does. And I think it would be easier than 100 XP * (level + modifiers). But it's only easy if you use monsters in the MM.
There's a whole other discussion to be had about how to award XP to get faster leveling in PbP, if that's what a DM wants. Marullus's sandbox does a good job of it, I think, using rules he adopted from Keehnelf's game:
Basically, he awards XP for almost everything: recovering treasure, discovering a new location, defeating monsters, uncovering clues, and "miscellaneous accomplishments." In AleBelly's game, he awarded XP every now and then with the passage of real-world time.Marullus wrote:The party earns 1xp per gp of treasure and saleable loot they return with or recovered and used during the expedition. Additionally, the party receives xp for enemies slain or otherwise defeated. Then, the party earns xp for locations of interest uncovered (100 x the general level of the location) or for good clues about new locations that they do not visit (50 x the level of the location).
Finally, the party receives xp for any miscellaneous accomplishments achieved during an expedition (GM's discretion) based on the scale or scope of the achievement. For example, killing 50 goblins would net xp equal to 50 goblins but if that were the entirety of a tribe and the group' so tended goal was to eradicate the tribe or drive them out, that would merit an additional xp award.
IMO, if you want to accelerate leveling in PbP (and you might not!), you have to do more than just increase how much XP killing monsters is worth, because killing monsters—i.e., combat—is the slowest thing in PbP. The most effective way I've seen it work is with DMs who award copious amounts of XP for everything they can think of.