The thing is, the saucer is so immense that not even its designers could think of enough stuff to fill it with... That is, I doubt Probert designed complete innards, and when Whitefire and Sternbach did their respective takes, they had to resort to massive empty volumes dubiously reserved for purposes that did not really call for them. Indeed, Sternbach's official blueprints leave the very area beneath the mystery windows undescribed - there's just a big cavity in there, perhaps because he didn't want the secrets of the saucer warp engines to fall in Klingon hands...
So the very reason the saucer is that big might be because Starfleet wanted warp engines in there. The 1014 crew and passengers are just rattling in the remaining spaces, waiting for the 10,000 evacuees or troops to come aboard, or for some other eventuality to fill up the volume defined by the combination of a warp drive and a nicely elliptical saucer big enough to house that.
I basically agree with you. Though I think the Whitfire Blueprints had filled the saucer with much good stuff - It just wasn't that detailed-, I agree that Sternbachs blueprint had a lot of redundant detail.
they had to resort to massive empty volumes dubiously reserved for purposes that did not really call for them.
Do you mean, it didn't make sense where they placed things?