In my response I was addressing the specific phrase “let or hindrance”; that let has historically been auto-antonymic is incontrovertible and well-documented and (whether rightly or wrongly) I was interpreting samatman’s comment as referring to the two specific contexts where I say it is still exhibits its historical auto-antonymicity.

I was. I'm still convinced that the folky etymology we've found online for tennis is wrong, because "serve, let, fault" are all about the server. But that's hardly relevant.