Are maple necks really always brighter than rosewood necks?

Wellsir, in an a/b test players were unable to tell a maple neck from rosewood, either playing live or listening to the same necks on a recording.

And as I've said before:

(a) Maple just isn't that bright sounding of a wood to start with, (other makers have said similar things). It's actually fairly neutral. Hard ebony, and especially Pau Ferro, can be very bright.
(b) Most 'bright' Fender guitars remain bright when we swap necks, if they are set-up the same.

On a Tele, you'll likely find some more twang from shimming the neck and raising the bridge saddles, and using smaller diameter saddles. Those are the kinda things that make more obvious differences in tone, and explain (b) above.

I think the whole 'maple is brighter' rumor started in the 60's, when there were only rosewood Fender necks available, but mostly for the reasons above, and the fact that most 50's maple necks are about 50% thicker/fatter, used one-piece construction and have the narrow frets 'glued' in place by the lacquer. It's more likely those differences that can make some of necks brighter and not the bit of wood used for the fretboard..
Over the years I've made quite a few necks and guitars and done quite a bit of work involving electric guitar tone. So while some of this is merely my own opinion (and I could be wrong), it isn't just based on idle speculation either. ;-)