On a broad scale, yes. But it also proves that the efficiency of particular languages depends on the problem at hand. For example, if your problem is searching for a pattern in large strings, a simple Perl program using the builtin regex support will easily beat a C/C++ program that hand-rolls pattern matching, because Perl's regex engine has been optimized for over two decades.

On the topic of mobile devices, I recall the Nokia N900, which ran mostly C and C++ software. Its UI performance was comparable to contemporary smartphones even though it only had 256 MB RAM and a single-core 600 MHz CPU. (Of course, a major part of today's phones' slow UI is all the bullshit and spying that apps are doing in the background.)

If your primary metric for good software is {speed,memory use,energy efficiency} then yes.

Linux and Darwin is written with C. They are the OSs of Android and iOS.

But would be nice to have some mobile apps written with C.