The only mostly empty loadouts that I've found effective enough to use are the 2x plasma odyssey (mostly because it has 10 billion small energy slots but only needs like 4 for decent PD, and small energy assault weapons are a waste of OP) and the astral (because bombers + astral ship system are better than pretty much any weapon). I think generally, there are good uses for the majority of slots on ships.
The AI backs away from you at max speed as soon as you try to approach it?
No. As soon as i am within its gun range. If you know of any non-SO cruisers that have an as fit range of non-pd weapons under 450 then they might continue to advance but as far as i am aware none exist.
They
start to back off when they are within gun range, but they have acceleration so they aren't actually going at max reverse speed for a while after they make that decision (and might even be trying to flak you instead of run). In my experience, good piloting lets you mostly avoid the 'chase scenario' where the enemy is out of range and running at max speed unless they already have a significant acceleration and speed advantage. I just tested it in the sim: I fought a falcon with a SO eagle and no speed skills. All I did was bait out the enemy maneuvering jets by backing up and then full forward with my own maneuvering jets. I recorded a video
https://youtu.be/sEWufRV-xA0 and the time between when my AC started firing and my DLMG started firing was ~.7 seconds. I was only going my top speed of 173 so it should have taken 1.5 seconds if the falcon was in full reverse, .87 seconds if the falcon was stationary meaning the falcon must have been moving towards me slowly. Even if my timing wasn't perfect (it's hard to see exactly when shooting starts with the shield effects, although I was going frame by frame), the falcon was definitely not in full reverse, the engines make it look like it was close to stationary which is consistent with the timing.
It's pretty easy to play around range disadvantages in this way, at least for the player and the raw speed difference between ships is not a good indicator of the actual time it will take to approach ships.