I don't know from which alternate reality you are taking this information, but its not really how it was. Apple's two line of products were 1) consumer — cheaper, less powerful, more mainstream components and 2) prosumer — expensive, better components. At some point the consumer-level MacBook Air has replaced the (plastic consumer-level) MacBook 13". Then we got the new 12" MacBook which is about to replace the MacBook Air.
As to the MacBook Pro — it was always slimmer and lighter than its category average, since that was always its design goal. It didn't stop it from having very good CPUs (and an okdish, but mid-range at best GPU). So Apples obsession with thin and light is kind of old news — the've been doing it for decades. The MacBook Pro was never more powerful (in relative terms) than now. Its still fastest consumer-level CPUs and a decent mid-range GPU. I really don't understand where this "prioritizing form over function" suddenly comes from. Just because its thinner? Sorry, that is just silly. Judge a laptop by its specs and capabilities, not by how thin it is.
P.S. Here is the original press release from the first ever MacBook Pro introduction in 2006:
https://www.apple.com/newsroom/2006/01/10Apple-Introduces-MacBook-Pro/
Count how many times the word "thin" is used
[doublepost=1524580224][/doublepost]
The choice is more or less the same as last year or the year before it or the three years before it. As some folks were discussing in one of these threads, the competition is catching up. Not long time ago, Apple was the only maker of premium laptops, everyone else just went as cheap as possible. Now, Dell, Microsoft and the others are getting more confident in the premium segment as well. Still, the tradeoffs between the XPS and the MacBook Pro are the same as for the last few years — the first has slightly faster GPU and is cheaper, the second is lighter and has longer battery runtime.