"Buffs" are done outside of combat
"Debufs" on enemies are often part of standard combat rotations (e.g. Shatter Shot or Sundering Assault)
"CC" happens right at the start of an encounter. Only rarely is it needed mid combat.
Depends on abilities. You can put a -armour debuff on all foes, not only the one you are dpsing, and there are times when you have to use short ccs/protection buffs to help comrades. The are debuffs which are useless for your dps but help tank/healer, like -accuracy. Or you can ignore self defence and put everything to dps, blaming a healer if you die. Point is, dps is a subjective stat to grade an actual perfomance. I.e. you can throw aoes to get better total dps numbers, but the actual contribution to the fight effectiveness will decrease. A good dps is not the one which has better dps numbers. Oh, not doing interrupts is also a good way to increase dps.