Hey! Good question - and remarkably enough, no one has ever asked it before - including anyone on the team!
The only person who can really answer this question is Eder - he is the one who decided for most ships. What you need to also keep in mind is that Standoff's huge cast of ships was not entirely intentional. We knew which ships we need, and those were made first - but then, a huge number of ships were added at random times during production... because Eder really loved modelling them, and if he cooked up a WC1/2 ship in his spare time, why shouldn't it appear in the game?
Why no Paradigm? I suspect that Eder just thought it looks weird and doesn't really fit in with the other WC1/2/Priv ships. It does seem rather unique, right? I guess it would have made some sense to use a Paradigm during the first episode, instead of a Gilgamesh - but of course, the idea was that we'll need a Gilgamesh anyway for the later episodes, while a Paradigm... well, nobody would really know what to do with it.
The big question with the Paradigm is: what the heck is it? Is it in fact a destroyer? Or is it a corvette? Or is it... a frigate? The description calls it a destroyer, obviously, but you know, maybe that's just some propaganda thing. The fact that its Kilrathi analogue is the Kamekh, combined with its weak shields (that do not require torpedoes to penetrate) makes it seem more like a corvette. You could argue that the fact that its shields are penetrable in Priv is just an indication that we're getting closer to WC3 in the timelione, of course. Finally, the game files internally refer to the Paradigm as a frigate. Ironically, while this is least relevant (who cares? This one's a frigate, another ship's called a clunker, they're just internal filenames), it actually seems to be the best description to me. The Paradigm feels more significant here than a corvette (though I suppose End Run's corvette seems much more impressive than anything we've seen in the games as well).
Oh, one other thing. Had the Paradigm indeed been a good replacement for the Venture, that would have actually been a point against it. We didn't want to replace the Venture. We loved the Venture, and I personally wanted to have it in the game a *lot*, because it had been so terribly neglected in WC1
.