There will be always People with different opinions. Both sides will always have their points, but in the end it shouldnt break the Gamebalance, which Levelsync will do.
It did affect the gained SP. And that is the way it should be. After launch the gained SP was really messed up and it got fixed a while later. But the PL-System ( which i also dont like ) broke the Balancing imo and made it extremly fast to rank from 1 to 50. Yoshi said 1-3 Month would be ok, but it ended up in 1-3 Weeks.
You dont realize, that Levelsync will cause a lot of Problems. How does it effect me? Simple said: As soon as i will look for a Party, i will have to deal with People which will stay in lowlevel Places. ( Like it was in FFXI ). Even if you say i can "avoid" that, it is simply effecting me in looking for a "normal" grind Party, which will go out into Highlevel Places. ( Like it was in FFXI ). I NEVER had XP-Parties in Xarca/Glacier/Bibiki/KRT and so on after Levelsync took Place, just because people went lazy and stayed at Quifim/Jungle. They didnt learn to play their Job, they didnt had full ranked Skills, since they were synced down. So it happend that you had People with Level75 Jobs, who didnt have a fucking clue what to do and were totally useless in Endgame, since the Skills werent maxed out. ( My Spells dont stick ?!?!??!? Go get Skillups, damn it !!!!!! )
Help out lower levels is the only Reason i always hear and maybe could understand, but basically the PL-System ( even if i dont like it ), is actually doing exactly that. We also had PL's in Valkurm Dunes and it was fine for everyone.