That's not the proper use of "antiquated". Entertainment does not ever get "out of fashion" and for something to be outdated there needs to be a modern version that is superior.
In other words, for the sub-job system you speak of to be viably considered antiquated, there needs to be a different kind of sub-job system that is more user-friendly/enjoyable. You cannot say that the sub-job mechanic itself is antiquated, ever, without being plain wrong.
You're free to hate this system, it's your opinion and your enjoyment. I on the other hand like this system and it irked me that the "necessity" in FFXIV was so low when I begun playing. I always wanted the multiple classes to be more tied together, not less. And they completely removed it...I say, what's the point of making a Final Fantasy game and then remove the very thing that makes Final Fantasy series games different from rank and file RPG's?! This is not Final Fantasy game in anything but name. It's a good RPG with good story, but it have nothing that makes Final Fantasy what it is beyond that and some aesthetics. Not even skill effects are anywhere near other Final Fantasy titles.
No, it's not nostalgia. It's entertainment. If I'd say that I cannot understand how anyone can still want RPG's in this day and age when all the rage is Battle Royale, Idle games, mobile strategy games and MOBA games, I'd be rightfully laughed at. You are doing the exact same here, completely dismissing a core concept that simply cannot become outdated.
This can be done well and it can be done poorly. But the idea behind it is at the same level as tactical strategy games, turn-based strategy games, real-time strategy games, arcade races or simulation races, isometric RPG's, third person perspective RPG's or first person perspective RPG's etc. It's a design type within the general genre of RPG.
And I like it now for the same reasons I liked it five, ten, fifteen years ago. Because it's fun. Because I like mix and matching stuff. Final Fantasy Tactics series are still one of my favorite games ever, not for the stories which weren't all that fun in comparison to some other games, but for the mechanics that these three games offered. I liked trying to figure out how to get an overpowered Calculator in the PS original, without putting myself in a bind (random encounters were based on the highest/average level among your party, so you could power-level a single character in a single fight to high heaven, but as a result you would be absolutely obliterated in the first random encounter). I liked making powerhouses that could deal with individuals or groups at any range in Tactics Advance. The final game in the series actually took some of that freedom away with its changes to mana system (start at zero, rather than start from full) and all-around "balancing", but it still offered customization that allowed me to make a party however I wanted.
Also, there is no such thing as "unique but balanced". It's either unique OR balanced. There are only so many factors that can be modified, even less of them are left.
Range (close, mid or long).
Which of the trinity.
Damage in burst, or in constant.
AoE heavy or single-target heavy.
Magical or physical.
Support heavy or raw damage.
Heavy heal or heal and shield or heal over time.
High HP or high damage reduction.
And...that's really all. The last two don't even apply to DPS, each applies to only one role. So that's six factors for DPS, seven factors for tanks and healers. You simply will not be able to maintain balance with variety. There's only so many ways to make damage dealing skills when there is no difference between the damage types anyway. They removed elemental effects so all the skills are one and the same, with different potency. There is still a difference between magical and physical to account for magic classes lack of auto-attack, giving them more bang for the buck on skills, but that's about all.
They should go the other way around, actually. Embrace the fact that classes can be changed freely and make classes that are simply fun even if they lag behind on power. In lower content they can be enjoyed as is, in higher content the players can just switch. But of course...they won't. Cause they listen to the "I don't care about multi-class system, I want my class to be at the top in all content, period, cause I like it the most" instead.