I don't have any issues with leveling in the game currently. I'll admit; it was a bit slow in the beginning since where were only a few ways you can level. Since the start of the game until now they've provided far more options and have made it easier to do so. If you're looking for getting out into the world hunt marks are a great way to explore the game, as well as earn EXP, gil, and seals. As mentioned before, Palace of the Dead and Heaven on High provide alternative options. If you get a good group you can rake up EXP like crazy. One of the old school ways is FATE grinding, especially in Shadowbringers since they created Bicolor Gemstones. It's all a matter of figuring out which way is more enjoyable.