Don't worry about them. For PvP players, any ship which isn't at least 80% loaded with HRPs and MRP's, ideally some SCB's, as well as engineered isn't considered "properly" outfitted. The only gameplay they recognise is combat.Since you're talking about outfitting, Let me just add that my krait was outfitted for mining, where all of my optional internals were taken up by cargo racks, limpet controllers, and a fuel scoop.
I was flying a CM3 and got attacked the other week. Like you, I lost the interdiction despite being near perfect (and I haven't lost to an NPC in as long as I can remember) - in fact, when I realised that I was going to lose this no matter what, I submitted, but instead, the game treated me as having been fully interdicted (ie, crash out of SC and long FSD cooldown). So I'm guessing it was the attackers' PC which dictated whether or not I submitted, not my PC.
My CM3 (engineered shields, military hull, and a HRP) was down to 50% hull after one shot and destroyed on the second by a (presumably) well-engineered gank-Python.
So basically, what the PvP'ers say is ; even a reasonably (not fully) defensively-engineered ship stands no chance against a fully-engineered attack ship; certainly not if there's a size-class difference between the ships.
Could I have done better? Almost certainly; I have little PvP experience. Personally I stick to PGs most of the time until the massive disparities between engineered and partially or unengineered ships is removed from the game. There's zero skill involved in shooting fish in a barrel but some people get their jollies from it. I refuse to be a fish except under exceptional circumstances such as the other week when I fully expect to get destroyed.
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As for the interdiction being not only slightly in favour of the aggressor, but also the bar continuing to go up in favour of the aggressor even if both sides are perfectly aligned, that really sucks; shame on FDev. If both sides are perfectly aligned, neither bar should go up. So what if the interdictions take longer? But at least remove the built-in "cheating".