In what way is it not? You'll consistently get 10 or 12 colors instead of getting an inconsistent set of colors, for example.

But I only want the element to be the color it IS, not a range of colors it could be. Whats to stop a dev using $concrete when they should be using $cloud? or $linkGray instead of $headerLinkGray?

these inconsistencies compound, especially across teams.

Nothing would stop them from choosing to use cloud vs. link gray but it's far easier to identify and fix those cases than it is to have #CCC, lighten(#CCC, 10%), etc. around the codebase. This doesn't fix human error, just reduces it.