>The 12" Macbook was a perfect example of this: in the quest for thinness, it was simply too much compromise.
I think you need to put it in perspective. The MacBook Retina was just like the first MacBook Air, it wasn't the best or good enough when it launched but It was designed with technology coming soon in the next 2 years, the promise of Intel 10nm in mind and WiFi 6 / 802.11ax. Both were suppose to come in 2016 / 2017. The 10nm, and its subsequent 7nm CPU would give Quad Core Intel CPU in a fanless design that is as powerful as a 2014 Quad Core MacBook Pro. And 802.11ax, 802.11ad or 802.11ay in the 60Ghz. The first would finally give Gigabit Ethernet speed in a wireless environment the 2nd ones would allow Wireless Transfer in dozens of Gbps within direct line of sight. For Macbook's target audience, those computation power was more than enough.
Fast forward to now, not only Intel wont have 10nm ULP CPU in massive quantities by end of 2019, it is likely not even the same 10nm as it was originally scheduled / promised in pre 2015 meetings. WiFi 6 / 802.11ax has been met with delays after delays to the point the Working Group literally force their way out push for commercial roll out. Last time I checked their meeting notes it still has thousand of issues unresolved. Much more than all the previous Draft WiFi standards.
One theory I have, was that Apple could not afford to anger, complain or make any signs of hardballing in their Mac department as they have a much bigger grand plan, to work with Intel together on the iPhone Modem and attack the Qualcomm business model. Since they have to decide their iPhone 7 Modem in Summer 2015, the thoughts and grand plan must have happen earlier, some evidence suggest this started in 2014 as it was shown in the case between Qualcomm and Apple.
And it was one reason I suggest switching to ARM on Mac doesn't make sense because Apple relies too much on Intel's Modem on its iPhone. And the iPhone business is the bread and butter of Apple. Now that everything has been settled I strongly believe Apple Mac will announced their ARM move within 30 months. But this is another topic for discussion.