There's a nice interview with Mike Clark where he talks about this a bit. His take basically matches this. He says that, in his view, any efficiency benefits of ARM are just that's been the market for ARM. In his view, if x86 had a market motive for ARM levels of efficiency, they'd be able to deliver it. But, historically, the x86 market wants performance more than efficiency, so that's what it gets.

https://www.computerenhance.com/p/an-interview-with-zen-chie...