Ada is a higher language weather or not it has linkage to C or not. The UNIX community cares about performance, performance, performance.
Is Ada less performant than C? I know it has bounds checking, but that can be turned off for "shipped" software. Does it have some features that incur a runtime cost and that can't be disabled?
With all the runtime turned GNAT can/should produce code with in a percent or two as fast as GCC (they share the same backend).
And Ada has a thing called SPARK which is a set of compiler checks to formally verify your code so you can provably turn off those runtime features safely. https://en.wikipedia.org/wiki/RavenSPARK
As you can see from the article (not that you seem to have read any of it), ATS can express C, and optionally prove low-level stuff about it.