There are 26 fundamental constants, ie values that can not be determined from theory alone and need to be experimentally measured, which all other constants can

There are 26 fundamental constants, ie values that can not be determined from theory alone and need to be experimentally measured, which all other constants can be written in terms of. And it's not even a specific 26; 1/c is just as valid a constant as c, and you could rewrite any equation to use that instead of c. For ratios, the constancy of the ratio is exactly what they seek to test.