What you're saying is essentially that Cargo follows the principle of "easy things should be easy; hard things should be possible". CMake, Autotools, Make, etc.

What you're saying is essentially that Cargo follows the principle of "easy things should be easy; hard things should be possible". CMake, Autotools, Make, etc. do not follow this principle; hard things are possible, but easy things are not easy. This might look like inflexibility, but I don't really see that. Cargo does let you do hard things; it's just that it has a "normal" workflow as well, which makes the simple case simple.