Just a random thought. It almost seems useless to buff and debuff most of the enemies as killing them outright always seems to better in the long run. Not only that, but some of the debuffs also can fail.

I love this game to pieces, I just wish more of the skills felt useful.

If only we could kill them outright... but in higher level delves that is sadly not feasible. A giant with 144 HP is not simply slain. Debuffing him is quite useful in that situation. (eg, decrease his damage output to 0 with the Occultist.)