I think we should avoid talking about people as being either on or off the autism spectrum. For the term to be useful, "autism spectrum" should refer to a spectrum that includes everybody. There's a cluster that we can call neurotypical, and off in one direction we have some people who share a combination of traits called autism, and if you draw an imaginary n-dimensional line between them, you can meaningfully talk about where any particular person is on the autism spectrum.

"Autism spectrum" should refer to the spectrum of variation in the traits that autism affects. The current usage is confusing and doesn't do much to help us talk about the people who are (as you put it) only about a standard deviation or so from the norm.