This sort of design would not work in FFXIV, and it would lead to people locking players out of groups because they don’t have key skills for each job. Especially for some of the utility jobs like physical ranged or AST. Why would you want a DNC that doesn’t have Standard Step or Technical Step in their kit? What else are they bringing to the group? Very little, if we were to look at the job as it stands now. DNC’s value comes from it buffing the party—without those buffs, it’s a very gimped DPS. Its personal damage is certainly not high enough currently to warrant bringing a DNC that doesn’t have keystone abilities. Why would you bring an AST if it doesn’t have its cards? Just bring a WHM. Granted, AST’s healing toolkit is more versatile (assuming the AST in this system bothered to unlock all of its healing toolkit abilities), but the WHM would technically bring more as it has higher personal damage than an AST. This really goes for all jobs. Why bring a BLM that doesn’t have Fire IV? A SMN without Summon Bahamut (or even egi summons period)? Or a DRG that only has it’s most basic 1-2-3?
This game is also not designed with branching rotations or branching builds in mind. For the jobs in this game, it’s not an option to have X skill, but not have Y skill or Z skill when it comes to max-level play (leveling is, obviously, very different given how skills unlock—to a point; it is still expected of you to keep job quests up-to-date with your current level to ensure you have all the skills you’re supposed to have). The jobs’ kits are so intricately designed with each piece in mind, that it would feel incomplete to be missing skills—a good example of this is BRD pre-level 52 where they only have 2 songs in their rotation. There’s a 20-second gap where you don’t have a song active, and the rotation is incomplete. And feels incomplete. Imagine that at level 80. It would compound the feeling of incompleteness even more so. And it would lead back to my first point: why would groups take a BRD with only 2/3 songs unlocked versus one with all 3 unlocked?
You actually saw shadows of this in Heavensward when DRK was released. Back then, Provoke was a cross-class skill that you had to level GLA to level 22 to obtain. It was very common to run into DRKs that had not leveled their GLAs, so they didn’t have Provoke to take bosses or mobs off of party members. And they were, rightly, criticized for not having that skill. It’s too core to a tank to not have. To a lesser extent, you could see this with healers and Swiftcast, which required level 26 THM. You honestly saw this with crafters as well until the developers streamlined everything. Why was it recommended to level all your crafters in ARR and HW? Because you had to cross-class skills from other crafters to do high-end rotations.
BLU is a different example where it was designed to sort of have all these different options for skills and rotations and “builds”. Mathematically, I am sure there is still a “most optimal” rotation for each kind of BLU (tank BLU, healer BLU, DPS BLU, etc.), though. But since BLU is basically a gimmick job that cannot participate in battle content normally like all other jobs in FFXIV, it gets away with this design. If BLU could participate in content like the other jobs, you would absolutely see people saying “You don’t have X-Y-Z skills? Why don’t you have them? Go get them.”. Especially at high levels of play. I think it’s less elitism and more so the fact that, by playing a job with only half a rotation, you’re griefing the rest of your party and basically forcing them to carry you.
FFXIV as a whole was not designed for all jobs to have BLU-esque “skill books”, and I don’t think it would be healthy for the game to switch to this. Not when the current battle system is this deeply established—this game isn’t exactly young.