When there are so many variables in the construction of an electric bass which contribute to the final sound, it baffles me why some people obsess over the sonic signature of fingerboard wood as though it’s the be-all and end-all. A luthier building a bass is arguably more likely to use a particular section of rosewood because it has a visually appealing grain pattern than for how it sounds. The best looking grain doesn’t necessarily equate to the “best” sound. And there’s no real way of knowing how it’ll sound until you put the damn thing on the bass anyway.
Since wood is an organic material with natural variances, It’s possible to find a particular sample of rosewood which is sonically brighter than a particular sample of maple. It is something of an imperfect science, given the cocktail of contributing factors.
I just choose whichever wood looks best on that particular model of bass and get on with it. After all, you can’t exactly change the fingerboard on your bass once it’s built (well, you can, but at great effort and expense.)
Call me a heathen but I’m of the opinion that simply changing your strings has way more of an audible effect on tone than whether your bass has a maple or rosewood fingerboard - or any other wood for that matter. And then you get into pickups and circuitry, active preamp characteristics, capacitor values, VVT vs VBT on a 2 pickup bass, selector switches vs blend pots in terms of how they load the pickups, high mass vs lower mass bridges, nut material, nut only vs zero fret, fret material, headless vs headed. The list goes on.
For what it’s worth, I used to prefer the “clean” look of maple boards but now much prefer my basses to have darker fingerboard woods like rosewood/wenge/ebony, simply because I prefer the visual contrast against the strings and frets - makes it easier for me to glance down and know where I am faster, especially in certain lighting conditions. Might sound weird to some but hey, it gives me some degree of comfort!