I believe the whole odd number of lt and lt commander and such was all due to the maquis crew. And the maquis were supposed to be primarily officers who went out on their own... it ties in with suddenly having so many officers on a ship.
And voyager being larger... the point of the show was "the lone tiny ship lost far from home in a galaxy far far away with no hope of getting home"
If you look at every single "Lost Ship" show from the last 40 years worth remembering, they all at least bothered to make them be really huge ships with unique abilities.