AMD's CPUs do many fewer instructions per cycle as Haswell (in some cases half as many), not to mention Skylake. You can't really compare GHz between them. And

AMD's CPUs do many fewer instructions per cycle as Haswell (in some cases half as many), not to mention Skylake. You can't really compare GHz between them. And releasing a new architecture is not exactly feasible if they want to stay in the server, workstation, and desktop markets. That idea behind Itanium actually was to get faster by dropping x86_64, and we see how poorly it worked out.