It would not be hard at all to fix this problem.

Make it where people outside the party cannot attack mobs simple as that and if a high level person hits a mob SP is calculated off that even if they leave the group. There is literally NO reason at all for the current system. The excuse it is for large scale content is void because SE done it with a claim system already in the past. 30ppl dyna, 400+ people besieges. So it is doable... SE themselves have done it before.

SE needs to scrap Pwrlvling and add in XI's level sync system. That way people can help their friends level up without then standing there while a mrd kill everything.....Gather mobs => rank 50 Drops party => Rank 50 kills everything => People still in party gets 200k/hr sp at level 2. <= that is stupid and should of been emergency patched as soon as SE learned about it honestly it is an exploit. Make it where you can Level Sync to temp lower you level a person in the level you can level with them. What pisses me off more is GMs stating it is not against ToS and is working as intended... why did the devs change it from before then.

All in all Pwrlvling I see no issue with, but the current pwrlvling is broken beyond belief. Pwrlvling should not increase SP gain 20fold. Pwrlvling should be limited to outside curing lowbies to help THEM KILL THINGS, not you doing all the work.