Like most traditional MMOs, FFXIV trickles job abilities to the player as they level up, rewarding advancement with a more complete vision of how to engage in combat. As the level cap increases and classes are reworked, this often means that there are fewer core buttons to spread among a multitude of levels, causing large portions of the leveling experience to feel "thin" or incomplete. This is exacerbated by down-leveling characters participating in roulette content, meaning that a player might be thrown out of a well-functioning job several times a day.
To illustrate, let's look at a job that levels gracefully (BRD) versus one that levels terribly (PLD):
BRD is built around DoTs, songs, and procs. Already by 30 and your first step into the true job, you have one song, two DoTs, and multiple procs to look out for. At 50, you get enough songs to cover 75% of combat, multiple AoE attacks, and a party buff to deploy during burst windows. By 56, you have three songs and your DoT management button - your class vision is fully fleshed out. Between 56 and 90 you add a builder/spender gauge, an additional party buff, some utility, and traits that add interactions to your existing kit. The class gets tolerable quickly and becomes enjoyable before the end of the first expansion.
PLD is much more backloaded. You do get a gauge and spender by 35, but it's a 6 second mitigation spender. Mitigation that is superfluous for the vast majority of roulette content. Sheltron gets a nice upgrade at level 82 that improves its impact, which is almost at the end of the leveling curve. PLD doesn't get an offensive resource spender until 64, and the AoE spender is at 72. This means that the majority of the leveling curve involves a 1-2-3 single-target rotation or a 1-2 AoE rotation with 3 oGCDs per minute. No resource management. No fun buttons. Just 1-2-3 and oGCD. Why not move the damage spenders to 35/45 like warrior? Or otherwise shuffle more of the kit to come online between 1-60, with the rest being flavor and upgrades?
Other MMOs avoid this issue entirely. Guild Wars 2 allows you to keep your full kit when you downsync, simply downscaling your numbers to line up with the content. But if this breaks the game's vision too much, at least restructure the job design to be less painful at the low end. Because FFXIV pushes players to downlevel for several roulettes a day instead of sticking to current content. And it elicits a groan if you try this on the "wrong" job.