Know what is useless? Your Class.

[Mychael]

They had an idea to go in one direction but didn't want to abandon all the existing assets from the 1.0 engine. So we're instead left with this mess of a compromise.
And when they finally do add more jobs, they're probably going to make sweeping changes. It's the same thing for Materia system, now they're developing a new one.

This is definitely not an issue of existing assets from 1.0. At launch, my CNJ had all elemental abilities and my THM all dark/light abilities. My individual skills (i.e. Water, Fire, Aero) would raise, and I could "spec" them. I also had a customization system through Guild Marks, through which I could buy unique skills... and even then, most abilities could be used regardless of your weapon (i.e. cross-classed to wherever you want.)

Hardly an issue of 1.0 assets being wasted. Yoshida completely scrapped every skill-related system from 1.0 before jobs were introduced.

When jobs were announced, idea was that classes were for solo content or small-group content because of versatility. An ARC could also be a backup healer and a CNJ could equip defensive abilities to save their lives. I know I went THM to Ifrit often so that I could have defensive moves to mitigate Hellfire, and cure for those OSHIT moments. The reality of present-day FFXIV is that the game is so easy that there's never a need for those "backup" plans, so higher DPS is always preferable.