But a random C compiler reimplementation isn't capable of compiling most of the other parts of
the stack in any case. GCC can be compiled with just about anything that supports ISO C, but
you'll need to reproduce a lot of GCC's (largely undocumented) foibles and language extensions
before you can compile, say, the Linux kernel with it.
I don't really see why the complexity of the *compiler* is relevant anyway. It's not as if GCC
is going to abruptly go away or stop working, so its complexity doesn't negatively impact you