Here you say "I believe" but the title says "proof"... which is it?
As others have said, I'd take the "proof" lightly, you cannot just compare two basses and conclude one part was what made the difference.
But, I think your conclusion is probably correct in some way. It seems like the sound does tend to "follow the neck", something that I've read many times, and partially confirmed myself. I'm hesitant to say "wood X sounds like this, and wood Y sounds like that" because there is so much variation, but there are some general tendencies on average.
However, what it ultimately boils down to are the cliches. Try before you buy; you cannot tell what the bass sounds like from the specs. Find the right strings for the bass; the right strings can often help with the perceived deficiencies. It's all in the fingers; with some changes to your technique, you can make a bigger difference.