I'm afraid I have to agree with Dukhat on this one. The Maquis hull is far too specific a shape to ignore. It's just barley credible that it has a smaller, shuttle sized counterpart ("Pre-emptive Strike") that there is also a cruiser sized variant AND that someone welded it to an Intrepid saucer and it is still somehow a functioning starship just pushes it over edge for me. That aside, it would also have to have two radically different warp engine designs working in tandem.
I think the cast off hull/counter intellegence idea is the only one that makes any kind of sense.
As for the Elkins, I like to turn my head, squint and pretend it's actually Sternbach's Voyager prototype (which I happen to perfer as the design for the Bradbury.)
I don't have much of a problem with the Centaur being at either Connie or Excelsior scale. There's sufficient logic to support both possibilities. So either way it's still the Renaissance class.