Of course if anyone wonders why SMN and DRK would be similar, it is because of the following points.

SMN 2 handed weapon user = DRK 2 handed weapon user
SMN has MP = DRK has MP
SMNs avoid casting spells when they can (preferably keep the same avatar out and not resummoning) = DRK avoiding casting spells when they can (to not interrupt melee swings)
SMN uses JA's (BPs) = DRK uses JA's (Soul eater and such)

The jobs are played identical (except for the obvious differences in WSes and JAs). Run in, melee all you can, use JAs when available.

That said, it isn't the ONLY way to play SMN. You can sub WHM and heal, sub COR and buff, sub RDM and refresh, toss up alexander 2 hour and zerg, kite NMs, etc. But the very basics of the job, is very similar to DRK.

I also believe a DRK could sub WHM and main heal decently. But for some reason that doesn't make them mages. Go figure.