10 years ago LLVM was a baby and GCC was still on version 4. Intel probably have an advantage in areas where people pay them for it but GCC and LLVM are excellent compilers today.

Anecdotally, (ignoring that I'm still not sure whether to trust it or not) Intel stopped developing IACA and suggested (but not recommended) LLVM's MCA - which does suggest a changing of the guard in some way.