Hiya!
@
pming said he gives out XP for "roleplaying" to whatever standard he sets at the table. However much his post implies it's a stick, it's really a carrot - XP as an incentive to play in a particular way. You can choose to play otherwise and apply your skill to overcome the character's perceived shortcomings, but you may not receive as much XP as others who do play to the standard he expects. But of course you'd rather call it a stick because you already made your mind up about XP 15 years ago when you decided it led to undesirable level disparity or you dislike integers or whatever other grievances you may have. To the extent that your posts can be called clear at all,
that much was clear. Above, you double down on the level disparity objection despite obviously having no experience with it in D&D 5e. I do, quite a lot of it actually, and I know that claim is bogus. In D&D 3e and 4e, you'd have the shadow of a point. But not in THIS game.
That said, the lack of a problem with level disparity doesn't detract from the efficacy of incentives. People tend to do what they are incentivized to do. To the extent that players want their character to advance in skill and power and the means for achieving that is gated behind performing particular tasks, it is reasonable to expect they will do those tasks.
My "somewhat limited view" of milestone XP is taken directly from the DMG.
I'd just like to add another 2¢ to the pot here.

First, when I "give XP for good RP'ing", it's closer to a...hmmm..."level percentage bonus". If someone does a "bad job" of RP'ing their character, they don't get one. If someone does a "normal" amount of RP'ing, then they get a "+X%" that is based on their PC's level. If someone does a real "good" representation of his PC, he gets more.
Now, my bonus is also used for things like succeeding in some particular "goal"; in the last session I ran the PC's cleared out the upper levels of the dungeon, specifically the bandits and their leader(*). These bandits were a problem for the locals, and becoming a bigger and bigger problem as time went on. So, when they got back to town and rested up, the PC's got a flat "10% of Next Level". As we are playing BECMI, that meant that the Thief got +120xp, the Fighter got +200xp, the Magic-User got +250xp and the Elf got +400xp. That's what I mean when I say "+X% of level".
* I'd like to point out that they were just adventuring with no goal other than "exploring and gettin' treasure". Nobody hired them to do anything. But, their actions still resulted in a boon to the surrounding area...so, bonus XP. I felt it was important enough to note that PC's can get these bonuses without knowing it. If a PC is afraid of water, and the PC's have to cross/travel an underground river and lake system...and the Player keeps RP'ing his fear/dislike of water...well, bonus XP to the PC. This is an incentive to give characters "potentially detrimental quirks/drawbacks/flaws".
Next, level disparity as never, ever, been a problem except for when we were playing 3.5e and Pathfinder. Any other version of "D&D"...never been a problem. I've had parties of 14th, couple of 10th, two 4th and one 1st level PC/NPC's (as an example) work perfectly fine in BECMI, 1e, 2e, and Hackmaster 4th. Where I *could* see the level disparity being a problem wouldn't be a "system mechanics" problem so much as a "player personality" problem. Where I could see a problem is if a PLAYER is one of those who's mindset is basically "If I'm not doing equally 'as well' as everyone else in the group, then I'm not having fun". Fair enough, but that has nothing to do with mechanics. Luckily for me, my group (if/when everyone gets back together...down to just 2 players ATM, from 6), everyone enjoys playing their character without any serious comparison to other PC's.
Bottom line...for me and my group, RP'ing, Goals, Fun, and many other things contribute to potential XP at the end of a session. Some PC's will eventually end up higher level than others...sometimes drastically so...but it doesn't matter because everyone is having fun playing their PC the way they want. Hell, one player made an
actual torchbearer as a PC (not D&D; was Dominion Rules RPG...but still). He played that PC for about two months. His character could sort of do a lot of things, but not very well. But...the player RP'ed the character as mostly interested and driven to excel at being "the help". He held the torches, carried a lot of mundane equipment (rope, iron spikes, torches, tinderbox, lanterns, oil, rope, etc). He was a fun character and survived just fine.
In the end, it's not really about "how much XP you get" or "what level you are", but about how much enjoyment you are getting from the game being played. And I think we can all agree that having fun is kinda the goal of playing.
^_^
Paul L. Ming