I have to disagree, in the West Wallace definitley took more votes away from Nixon.
Definitely in the interior West, but not so much in the industrial Midwest and Northeast. Out west, Wallace's best showings were in working-class areas that haven't been competitive for national Democrats since the 1960s; most of Wallace's voters in these areas, almost certainly, ended up voting for Nixon (or Schmitz!) in 1972 and (with the possible exception of 1976) for Republicans since.
But in the critical states of the industralized Midwest and Northeast, Wallace ran best among
unionized working-class voters. I think that's the key difference, and indeed it was widely noticed that as Wallace fell in the polls in Michigan, for example, Humphrey rose- and ended up carrying the state thanks to his union support. A straight Nixon-Humphrey race would probably mean Democratic victories in Wisconsin, Illinois, Ohio, and New Jersey.