Games (many in C++ with one or two features beyond basic C). All kind of solvers. GPU programming.
C sucks when you need convenience of big standard library or safety above performance. There is nothing like C when you care about speed, memory footprint and efficient memory management. It's great other languages took over in areas C is terrible at but it's not like areas when it's the best and often they only option disappeared.
These specific claims are flaky at best but hard to argue over since anyone can construct enough cases for or against their position to be right enough not to change their opinion of C.
You can absolutely beat C in everything you list. And you also can't. I don't agree that C is the end all be all of performance or code size, except in a handful of cases where there's nothing else available.
Objective-C, Java, Swift, and C# have become massively successful as application programming languages because C is/was terrible at it. They learned a lot about how painful it was to do basic higher level programming tasks when you are restricted to C's semantics and memory model.
C is great but I don't think it's worth romanticizing since history has shown that C isn't that great for writing anything but systems code. Which is a restricted domain to begin with, and isn't even that attractive for it anymore.
The one thing C has over anything else is interop. The language of FFI is C. There's no inherent reason for that other than history, and it's not super broken so we're not going to fix it.