Actually, I'd expand on my original point a bit.
Currently, my most well-developed job is Dancer. I use a modest DD setup; Magian daggers, Charis +1 with a +2 tiara, Twilight belt, etc. It's not exceptional by any means. I usually set RR/GH/SS now that the Crit Bonus Damage cap's been raised.
When I join random pickup xp alliances on DNC, it's not uncommon for me to crit regular dagger swings harder than the weapon skills of half the DDs in the group. This isn't meant as a judgment on people without good atmas or patting myself on the back for being smart enough to set Razed Ruins when I zone in; it's just how Abyssea works. Whether it is good or bad, I can't say, but one thing that is crystal clear is that I can completely mulch any non-NM in Abyssea no matter how leveled in 30 seconds tops. So the question is: how many DDs like me does your Abyssea alliance really need before everyone's content with the XP rolling in? 4? 5? Maybe two or three BLMs for azure?
The point is, I don't need your level 70 dude with no good atma to melee. Hell, I don't need your level 90 dude with no good atma to melee. By all means do so; we all need skillups. But you are not, strictly speaking, contributing by doing maybe a fifth of my damage on a good day. Cry all you want about level 30s in Abyssea but the dynamic of an Abyssea XP alliance is not radically shifted by the presence of a few leeches.
What I DO need when I'm rolling full DD in an Abyssea alliance is targets. If you don't have good atma, you are INFINITELY more useful as a puller than as an actual DD. A full XP alliance is basically wasting its time if it has fewer than three full-time pullers, imo, and I grit my teeth every time I see a reasonably well-geared THF or NIN who, judging from their HP, has clearly spent some time in Abyssea and probably has decent atma relegated to pulling when the three or four people in Scorpion Harnesses could do it just as well.
If I join an Abyssea XP alliance on my main, with its capped XP and merits, I'm doing so for one reason: cruor. It's been my experience that since I can't reliably farm azure on my own, even a mediocre XP party can get me more cruor and TEs than my own meticulous play. In order to maximize my cruor, however, I need mobs. Lots and lots of mobs. Way more than I can get by one guy pulling one bluffalo at a time. Pull for me, level 75 guy, and I will get you all the XP you want on all the jobs you want and thank you for the privilege.