> The sum of a large number of small engineering improvements, coupled with a lot of component integration detail work, topped off by some very shrewd supply chain arrangements.

I think the vertical integration they have is a major advantage too.

I used to work at arm on CPUs. One thing I worked on was memory prefetching which is critical to performance. When designing a prefetcher you can do a better job if you have some understanding or guarantees as to the behaviour of the wider memory system (better yet if you can add prefetching specific functionality to it). The issue I faced is the partners (Samsung, Qualcomm etc) are the ones implementing the SoC and hence controlling the wider memory system. They don't give you detailed specs of how that works, nor is there an method where you can discuss with them appropriate ways to build things to enable better prefetching performance. You end up building something that's hopefully adaptable for multiple scenarios and no one ever gets a chance to do some decent end to end performance tuning. I'm either working with a model of what the memory system might be and Qualcomm/Samsung etc engineers are working with the CPU as a black box trying to tune their side of things to work better. Were we all under one roof I suspect we could easily have got more out of it.

You also get requirements based upon targets to hit for some specific IP, rather than requirements around the final product, e.g. silicon area. Generally arm will be keen to keep area increase low or improve performance / area ratio without any huge shocks on overall area. If you're apple you just care about the final end user experience and the potential profit margin. You can run the numbers and realise you can go big on silicon area and get where you want to be. With a multi-company/vendor chain each link is trying to optimise for some number they control, even if that overal has a negative impact on the final product.