Level sync isn't the (only) problem. There's a definite issue with power creep, too. New jobs get higher potency skills to start with, so they break old content like an eggshell.
Item level sync is also pretty terrible, especially at old level caps. Remember when Weeping City or Rabanastre or Hades had some teeth?
Unfortunately, SE would rather funnel XIV's profits into new failures like Concorde rather than actually put any more than necessary back into the main game that's actually keeping the company afloat, so.....