I'm a little torn on this matter. At one side we have Thm>Blm and Lnc>Drg like your examples where your job adds very little to what you actually do anyways. Blm's usual rotation comes from Thm skills except Flare, jumps are mostly useless and have no place in your ideal DPS rotation at all. At this point I just can't see how Thm and Lnc can be made a whole new experience with new jobs (granted they ever get one).

On the other side we have Acn>Smn/Sch. Smn has a plethora of problems on its own but the point is, Smn and Sch have very different play styles despite coming from the same class, and the execution of Sch is done very well (with as little as 5 additional skills). I believe part of this success comes from Arcanist class successfully paving the way for both jobs, as Smn you drop the healing skills and as Sch you drop the damage dealing skills (for the most part) and focus on what your job enhances.

I guess we'll have to wait and see.