It wasn't generally thought that amd/intel were unassailable engineering wise, just that sw compatibility, x86 patents and volumes were important enough that it

It wasn't generally thought that amd/intel were unassailable engineering wise, just that sw compatibility, x86 patents and volumes were important enough that it was economically hard to go against them. But other chips (eg IBM) regularly challenged them on speed despite relatively tiny volumes and budgets. And of course years earlier the Itanium debacle + exponentially increasing fab costs (favouring volumes) killed off most of the RISC competition. Trivia: Simultaneously to the previous Mac ISA transition, Apple acquired PA Semi who had a power efficient and fast PPC chip. Then, Apple decided to go to Intel anyway instead of betting on their new in-house chip. Discarding their newly acquired highly acclaimed chip design, they put the newly acquired semi team to work on the A series of chips instead.