I do believe the heat and thermal throttling complaints of their top tier MacBooks are a huge factor
I have experienced this with both my MacBooks - especially with resource hungry applications they start to feel like I could fry an egg on them!
With the continued desire to make these things even thinner there reaches a point that there will have to be a trade-off. Who knows, maybe they've had some huge breakthrough with their processors that I'm not aware of. I would be happy with that!
Maybe it's because I grew in the 80s, but I actually like my laptop to have a little bit of thickness to it. I actually really like the size and weight of the 2013 era MB Pro 15" models. I just like the substantial, tactile feeling. Perhaps it is just psychological and showing of my age?
There is no question an ARM processor properly designed will be far cooler and likely not throttle. They already did the bulk of the work for the iPhone and iPad and likely planned this all along.