Why do we have classes AND jobs again?

[Colvin]

Personally I've always preferred the switchable superset type of jobs which take considerable time to fully master (each class having 3 job branches, for example), but I'm excited for what they have in store for ARR as well.

I think this is kind of what they ARE going for (but 2 jobs per tree) at the moment. But do you mean 1 class + 3 jobs? such that there are 4 branches to the trunk or that when you move to jobs, the class is a trunk and you don't go back?

[Recycler]

the class is a trunk and you don't go back?

This. The jobs being a strict superset of the class, there is no reason to go back, but you can still switch to another class or job of a class.