What if we got the Sub-Job System in FFXIV?

[Freyt]

I don't like any example I or anyone else can think of, as this is a silly subject in my opinion, every job should be tightly designed in a way that it can work well with its own kit, otherwise you're just making every job feel like the same thing.

You're under the mistaken assumption that sub-jobs have to provide abilities that already exist. I think you could think of some kind of scenario involving sub-jobs that you would appreciate, and if you can't, then I would suggest that you're not thinking hard enough.