Endwalker has been available in Final Fantasy XIV for a few days now and leveling to 90 can be one of the goals that you have in mind. In an interview done during the media tour, Naoki Yoshida explained that the story of the expansion would be enough to reach the maximum level.
Completing the story and not clearing anything on the side will not get you to 90 though, in fact, you will be blocked a few times along the way. A leveling roulette, Khloe's journal, or simply a few Aether Currents quests will be enough. The exp gap is not that big and I personally didn't feel bad about it but some players could feel disappointed in having to clear side content during their story progress.
FFXIV Main Story Experience Issue
Here's Naoki Yoshida statement on the matter:
"In an interview conducted before the release of Endwalker, I said you could reach the level cap for one job by playing the main scenario quest. However, we have been receiving feedback from players pointing out that the main quest scenario does not reward sufficient amount of EXP to reach the level cap. I deeply apologize for the carelessness of my statement and the confusion caused by it.
We have been balancing EXP gain by taking into account EXP obtained by completing main quest scenarios, completing duties from main quest scenarios, first time completion of duties, average rested bonus, and mapping the realm, so that level cap could be achieved by progressing through the main quest. However, our calculations were slightly off even with the considerations above.
The team test played the update several times over, but due to last minute adjustments made to various content, a small margin of error occurred. We apologize for the issue caused by this. In addition, because of my ambiguous statement that specifically mentioned by playing the main scenario quest, I think many players believe that level cap can be achieved through EXP rewarded through quests alone. Again, I deeply apologize for the confusion my statement caused.
Besides main scenario quests, additional EXP can be gained to reach level cap faster by completing aether current attunement quests and duty roulettes two to three times on top of the main scenario quests. The actual amount may vary slightly depending on your rested bonus, but we’d be grateful if you could consider doing this.
This is a balancing issue rather than a bug but was exacerbated by my own careless comment. Once again, I apologize for the confusion."
Endwalker is the new expansion for Final Fantasy XIV, released on December 3rd. We'll do our best to cover all the new stuff and produce any guides you may need during the expansion, you can also take advantage of our many guides on content already available here.