First of all, maybe I'm misremembering, but I thought Swimmer963 was a "she".

Thanks for pointing that out; I've changed the 'he's to 'they's.

I am entitled to be bothered by it, and to correct it when I come across it.

Ok, but emotionally satisfying responses are rarely strategic responses. The positive advice in your post (this ability can be trained) seems like an afterthought. If you led off with that, you would impart the same content (modern composers exist and have comparable or superior skill levels) and far superior context ('I am confident and helping' instead of 'I am offended and correcting').