Isn't one of the "secrets" to AMD's post-486 success adopting the general approach the Pentium Pro took along with others in the 1990s, which in turn are based on IBM's 1960s Tomasulo out-of-order algorithm adding speculative execution? This general approach made all out-of-order speculative designs, including ARM, POWER and IBM Z vulnerable to Spectre, so I submit they're not "completely different".