I don't see it as an issue. For one, you can always invite low level players to a fate party (who says they need to be excluded since players come and go constantly once they get their Atma). If low level players are curious, all they have to do is ask a high level player why a bunch of level 50's are doing low level fates, and they will gain knowledge that when they hit 50 they will know what they need to do in order to be well on their way to their zodiac weapon.

It's really a great way for low level players to meet some high level players, maybe join an FC or linkshell and make new friends. It makes the world feel full, and will be a breath of fresh air from any new players coming in seeing active zones. I just feel there are way more positives than negatives with this.