I agree in the sense that FATEs are vastly better than other options, because it's basically a full quest's worth of XP *and* provides GC seals, all in a very short period of time, and often able to chain many together. It's extremely efficient.
The problem isn't that FATEs are too good, but that there are no other alternatives that can compete. I think they are necessary because there isn't any other content for second classes to XP through. There's only Hunting Log, dungeons, and FATEs; Logs don't provide that much XP, and dungeons are set in intervals. FATEs are far and away the best option.
One thing is that, at max level, there is a sharp drop off in terms of gil generation. Sure, you can farm items and sell things on the market, but that transaction is from one player to another, with fees on both ends -- ultimately taking gil out of the system. The game lacks any major source of new gil after quests are done distributing their Allagan tokens. So one alternative to FATEs would be some manner of gil income source that forces players to choose between XP/seals or gil.
Another alternative is just to remove the GC seals component from FATEs and keep only the XP aspect of it. But seals are slow from other in-game sources, and they would need to add some other avenues of earning seals.