Quick estimating (which is a different skill from calculating exact answers using pen and paper) is most useful there. People do carry computers with them these days and they do have calculator apps. Some shops I buy from do have unit prices for many items.

I think AI might be more of a problem, at least for some skills because it is not just doing a small unit of work. its more like the problem of doing more complex calculations. An example I have come across with calculators is students learning statistics without knowing how to calculate a variance, because they just put the numbers into a calculator. There is a failure there to learn the concept - they do not really know what a variance or SD is. I can imagine AI doing a lot of that.