@Peregrine:

The theoretical problems you proposed in the first half have more to do with job/class balance rather than problems with the SP system.


As for SMN burns, that was and issue caused by abusing level sync, call for help, and the EXP chain system. There are safegaurds you can put into FF14 to prevent abuse, like limiting the SP chain bonus to only consecutive enemy kills that are dlvl 7 or higher.

Ideally, the balance would be such: AOEing trash mobs for excessive SP isn't viable because it doesn't give enough SP per trash mob, and you get no bonus for killing weak mobs.

AOEing a mass of medium mobs for excessive SP isn't viable (unless you are good) since gathering them will take too long, and you'll probably die from all the attacks.