I don’t think it’s a question of one factor in isolation deciding what makes a bass work or not.
For about three years I played on several Poellmann basses owned by the orchestra I was in. Lots of air in the box from the deep ribs, but short body length and much too thinly wooded in the table. The result was a sound which just wasn’t balanced, very tubby and indistinct. The low b was loud but the sound the basses made wasn’t pleasant to my ear (or anyone else’s). They were also stiff and unresponsive. Those basses had a short string length, around 41” if memory serves. My big bass feels much more loose and responds quicker than those 3/4 size ones did and I’m pretty sure that’s to do with the fact that it’s more strongly built.
I’m pretty sure with the right geometry you could have a bass with a large body but a short string length which might give you the resonating chamber required to have the low notes sound full whilst also keeping the string length down. See this example. I have never heard or played this bass, though, disclaimer.
Euro 5
You’ll want to weigh anything that can be considered a contributing factor equally. As soon as you get into the zero sum game of compromising one thing to solve another issue, what you’re doing is knowingly overlooking issues you know to be relevant as part of a gamble.
As far as I can tell the safest way to get a five string bass to sound good is to have a large and well proportioned/thicknessed body and then learn to adjust to the compromises that necessitates from one’s playing. The string length could be any range of numbers according to preference and how well thought out the shape of the bass is according to that preference.