These numbers aren't comparable. You're equating membership of an actual Nazi group with being a member of a far-right party with historical ties to Nazis. A much more apt comparison to these parties would be to look at members of the GOP who support far-right policies, but that's hard to quantify.
FWIW, I don't have a particularly strong opinion on whether laws banning Nazi speech have a large impact on the number of people supporting that ideology. I don't think they increase the number of Nazis, and it makes sense to keep them around given the historical context of countries like Austria and Germany even if they don't have an impact on that number.
I do think you're quite far off the mark if you think less than 0.001% of the U.S. population identifies with Nazi ideology, while it's something like 1% for Austria and Germany.
