Having SMN and SCH both branch off Arcanist apparently caused some issues back in ARR though I think the main reason they didn't move forward to do something similar with the other base jobs to have them essentially have 2 role advancement options via job stones was the people complaining here after they got matched in DF with a SMN main that switched to SCH because they didn't want to wait for the DPS queue and hadn't bothered to gear the job or learn how to play it.