The thing is though most jobs in this game get balanced around high-end content because that is where it really matters, casual content not so much regardless of whether that is the majority.
You could add diversity to a single job's kit, but then there is so many jobs that players can find something that suits their playstyle. Chances are though that any attempt to do this would be self-contained in a particular kind of instance, Eureka (Pyros, Hydratos) being an example with customisable Logos Actions that allowed jobs to become much more hybrid. Open world content just isn't challenging enough for something like talent trees though, and party content players would mostly opt or expect certain loadouts from others.