I think you're probably right, but I do think guitar has one ease of use advantage over piano. scales and chords are "moveable" on guitar in a way they are not on piano. once you learn, say, the c major scale on guitar, you can just slide it up a fret and you have a c# major scale. same pattern and muscle memory. to do the same on piano, you have to actually keep track of what is sharp/flat in the scale. ideally you would develop a good understanding of the circle of fifths either way, but you don't necessarily have to on guitar.

maybe it makes no difference and I just feel this way because I've spent more time with guitars than pianos. when I sit down in front of a piano, I can't escape the feeling that it's biased towards c major.