I encountered the same thing on two different accounts. This happened to Commander Luke's team in both games: even if you deal incredible damage, the enemy doesn't die.
Ideas
Please read dengars zeta upgrade and then think about how many debuffs you are applying to him. Conquest enemies have jacked up health and protection and defense so the damage thresholds that might be fine vs regular teams are not going to be the same against conquest enemies. You either need to bring a debuff that stops healing or use a team that doesn’t heal dengar when you hit him.
The damage over time is more than 1660, I guess you didn't look at the picture. Neither zeta not debuff can explain this
It does. Every debuff you are inflicting is allowing Dengar to recover 3% Health and Protection. That's including every Expose from C3P0's unique and all those DoTs from your data disk setup. You'll also be performing a ton of crits which will also heal him.
Regarding your 1660 DoTs, those are never going to trigger as they pop at the beginning of a units turn and Dengar isn't going to take a turn due to all the turn meter removal on your CLS squad.
All these interactions are working as designed.
