Saying “you should do this because John Carmack did it” would absolutely be an appeal to authority. The fact that sometimes you really should do that thing doesn’t somehow negate the fact that the rhetorical strategy being used is ~”you should do this because an authority on the matter did it”.

The rhetorical strategy “appeal to authority” doesn’t have the conditions you’re implying about the proposed hypothesis being weak, or about the authority being illegitimate.