I get both sides of this. There's a major issue of what benefit the higher-level players get.
If they get equal benefits to a party their level, areas with optimal setup for exp parties would doubtless begin to see nearly all of the parties. Skill levels (Healing Magic, Dagger, etc.) in XI provided some balance as they would be capped as if you were the sync level. With skill levels abolished from XIV and the only "level" being the class level, there is absolutely no reason for me to not sync down to whatever camp nets the most experience. While not an issue during the explosion of parties that will accompany any massive influx of players, this means that after most people have their 50s, only the "good" camps will ever get used. It makes half of the world seem unused. People who played XI--how many times did you party it up in Rolanberry Fields or the Movalpolos? On top of that, many people will assume that a lv.46 conjurer who will sync down will have more skill than the conjurer their level, and pick the higher-level player over the one that needs the party.
On the other hand, if you nerf anything about the experience for upper-level players, there would be little point in having the system in the first place--while it would be great for those of you who say "I want to help," it might be just worth your time to powerlevel a party, depending on how/what they nerf. This would be fine for now, when there are players who want to help their lower-level friends, and it would remove the risk of misuse/abuse of the system. But later, when the feature should function less as a convenience for the nice players and more as a necessity for the isolated new players months or years after launch/rebirth, letting level sync nerf anything about the leveling process would just leave the aforementioned isolated new players in the same predicament they started with.
Just my two gilz.