Overall I've stopped using PWOs on my standard escort builds and I've gone solely with purple TT DOFFs to help make room for more copies of APB into my builds - its generally shown a much larger improvement.
The only problem I've encountered so far with Conn officers (Tac Team ones) is that the recharge buff doesn't kick in straight away - from Heretic: "Due to issues with latency and synching, the recharge reduction time abilities actually kick in 1.5 seconds after use of the power" - so you'll never quite hit the Global Cooldown with only one Tac Team.
That said, I'm currently doing the same on my Nebula; rocking a single Purple Conn DOFF alongside the two Projectile ones. APB really is that good. On an Escort though about the only other thing I'd want to take in the Ensign Slot is maybe a TS 1 or THY1 - if I could get away with dropping APO1 without using up a sci BOFF slot I'd be a very happy captain, but the only thing that comes close to allowing that is the Antimatter Spread Console, which is a good bit less reliable.
The only thing I haven't tried is 2 Torps / 2 DHCs, I'll give this a try at some point and report back (if I remember this thread).
No worries. I get what you're saying about long periods of doing nothing, but whenever I last measured the length of my combat engagements themselves (discounting probes) on IGE, CSE and KASE it was mainly structures, with Cubes and "Bosses" like Donata and the Carrier a distant second.
The only exception was whenever I was on Kang guard duty in CSE.
I tend to run at 2 Photons / 2 DHCs on my Guramba. The practical clincher is taking APB3/CSV2/TS2 over CSV3/TS3/APB1, as I'm splitting my damage output between Torps and Cannons, and the Torpedo Powers being "spike damage" buffs means they don't do as much for Photons as they do for Quantums.