They're almost the opposite of auto-attacks, though? A DoT is a snapshotted high-ppgcd attack with strength per use diminished if used too frequently and total contribution finished if used too infrequently -- essentially a soft-CD attack. Except, also, whereas AAs can only strike one enemy at a time and traditional CDs cool only one charge per action, DoTs can be present and can cool on as many enemies as they are placed.

And then there's the remaining target lifespan (TTK, time-to/until-kill) consideration, too...