> "A spectrum would involve everyone having the same problem to different degrees;"

I learned the opposite, that the term spectrum is used when it is not same problem to different degrees. That's how the autism spectrum was explained to me, because the problem differs over the spectrum. In opposition to "level" or "gradient", which is intended to be something more linear over the same dimension.

I believe this redefinition of the term comes from how a "rainbow spectrum" is perceived, as different colors (and not as it is defined, as a linear degree of wavelength)