I actually do think that people doing color work should own an accurate spectrophotometer
that they can afford. I certainly would not tell them to hold it up to their computer screen.
Even so, the real issue at base is that many people who use CMYK for a color specification
don't know that CMYK is a device dependent color specification that needs
a color space profile to give it meaning. If you have CMYK and a color space
profile, you can convert it to L*a*b* with something like
http://colormine.org/color-converter
which has a CMYK to lab converter that has many of the common CMYK color space profiles
that are in use today. Someone can take a converter like this, and then see what works based
on trying each of the available color space profiles with the CMYK they are working with. There
are also ways in Adobe, Affinity, and RIP software to cycle through the CMYK color space profiles
to get a visual rendition- provided the monitor being used has been properly calibrated and profiled.
I am concerned about the common acceptance of using CMYK without some kind of
color space profile to give meaning to the CMYK numbers. With Pantones in particular,
I can tell you that Pantone-provided sRGB numbers(based on the sRGB color space profile)
always converted to Pantone's L*a*b* for the swatch someone wanted. Pantone NEVER specified a color space
profile for their CMYK numbers. They could have set a better example, but chose not to. My
comments on Pantone are based on my experience of the Pantone Color Manager software,
which was discontinued in favor of Pantone Connect.
I should have mentioned the color converter and software approaches in my original message
to be more effectively responsive- thank you for your message.