This game rushes you to endgame though. It is not like FFXI (at least a few years ago) where getting to 75 on each and every class/job was a journey where you met many people. The main scenario speeds you to level 40~ (mostly through easy, forgettable filler quests, but there are some decent dungeon and primal battles in the mix) and then you have to fill the gaps with FATEs as you complete the rest (worst, but most rewarding content in the game - actually, worst content to ever be in a videogame with the name Final Fantasy in it). Other classes are FATEs the whole way through, which is even more linear (and nightmarish). Yoshi-P himself has implied that "the game really begins at level 50".
Unfortunately, the endgame is very linear (more linear?) in terms of progression and gear progression, with really no room allowed thanks to how attributes work (gear is all the same, just with higher "item levels"). This also means higher and higher items levels in a short amount of time (we are already up to 90, several tiers, and the game just launched), which means more content being outdated quicker (less variety looking down) and more gear checks (less variety looking up). Crafted gear would at least provide two paths (of the same kind), but those also required a lot of tomestones... the exact same thing you need for non-crafted gear. So, yeah. Linear is how you could describe this game.
One thing this game does is discourage the idea of actually making use of that "be any class you like" - effectively making the game more linear. It does this by 1) only having enough decent leveling content for one class and leaving the rest for FATEs (again... a nightmare even once let alone for every battle class), 2) endgame being an insane grind where every class shares a single resource (tomestones) for virtually of their gear.
EDIT: Cross-class actions not being used in combos is definitely a missed opportunity. In fact, cross-class actions in general are poorly designed when looked at a multi-class perspective. Those actions should be useful for every job that can use them (e.g. Cure should give something to Paladin to make them consider using it). It feels like the team, headed by Yoshi-P, inherited game mechanics they don't know what to do with. You can also see this with how simple combos/actions which make up a combo are now, how battle guildleves don't fit into the game (why are they limited when FATEs are EXP fountains and dungeons can be done multiple times?), and how crafters and gatherers are basically being throw aside for unnecessary "side-upgrades" in favor of dungeon loot (farmed through tomestones).