Delta also provides a hull resist to self/ally, while debuffing whoever is targeting them. This is why it takes second spot after APO for PvP.
APD & APB both have better durations than you suggest because of how they function in that they buff both the user/recipient as well as debuff the Target (APB actually reapplies to the target each time they are hit).
The main issue with their debuffs is that they are cleared easily and frequently by TT, so the window of opportunity is very tight, again why APD shines with it's self/ally hull resistance boost.
Given the fact that this person is using beams on their escort, I'm going to assume they're not PvP-ing much. (Beams have no place on escorts, especially in PvP) It is essentially saying, "Meh, I wanna be squishy and I really don't care to do a lot of damage. Infact I wish to be a martyr for the cause of "doing what I like". (Savor the flavor of that for a moment. Slightly harsh, yet very truthy, should go down easy.)
In regards to the AP convo, it's a VERY tough call. It is somewhat subjective and very situational. I think a lot of good points have been brought up regarding the different AP's including their positive and negative aspects. At a certain point, OP has to take this info and choose. I believe we may have reached that point... Red or blue pill?