I was pretty good at maths in school, and throughout my adult life there have been times when doing mental math has been helpful.

I must've saved quite a few minutes, perhaps even an hour total.

But it has never been that important, that using the calculator I always have in my pocket would've somehow changed anything in the moment.

In all, it actually doesn't feel like that helpful of a skill, though your milage will vary depending on your job.

In saying that, LLM's aren't going anywhere, and the panic around peoples stupification is probably a mask for ignorance or indifference which would exist regardless.