That concept sketch looks awfuly like a good portion of an excelsior class with the nacelles mounted on upside down. That's what makes me think of it as a kit bash.
The fact that they took the whole stinking warp sled assembly from a Runabout might have something to do with it. That's the part that would'Ve had to be replaced at any cost.
I deliberately made the distinction between those two images on purpose because the one from the front shows a better, more rounded version of the saucer with an integrated superstructure.
The engineering hull is somewhere between the Excelsior and the (too short) final one. For a long time the deflector assembly was halfway between the Galaxy and the final result, but the engineering hull in the concept version had the advantage of more integrated impulse engines, over a year before the Sovereign integrated hers more seamlessly (see the cutout that's partially obstructed by the right pylon in the following image).
Much like Mirandas and Nebulas the parts of the
CONCEPT(!!!) are modular and can be replaced more easily, whereas you either have to cut the final design apart or glue stuff to the hull like many Voyager episodes did (Scorpion, Living Witness, Endgame).
Voyager doesn't look modular to me, it looks very singular.
I'm not talking about what ended up on-screen but the original concept, which for a long time even had support for mission-specific modules, much like the Nebula and the Miranda.
Weren't the nacelles supposed to get around the 'damaging the fabric of space/time' problem they established in TNG?
Yes, and instead we ended up with kid-size highlighters.
It's a concept for a reason. It still needed more work and some parts just didn't work out, but it was a step in the right direction.