It is a bit of a tricky thing I think.

Sch does share a lot of spells and abilities with smn and vice versa. This is probably why sch can dps like it can is from the arcanist base spells and abilities, while on the other hand smn can't really use much for healer abilities it can help raise fallen party members when things go bad. I think the combination of the 2 compliment each other nicely, only down side to them being split from the same base class is you have to choose which stat to invest your bonus points into. If they could set it up where you can put points into both from a job stand point rather than as a class then you wouldn't need to pick and choose, they had adjusted the mind and intelligence stats based on job.