[toyg]

No, they chose between performance and thinness. Battery life would have been fine with a battery the size they used before.

[lethargic_meat]

Please, read this before commenting: https://en.wikipedia.org/wiki/Mobile_DDR

XPS 15 uses DDR4, is even thinner if possible than the MBP and has less than 4 hours of battery.

IMO MBP should be performance focused, being battery life a secondary concern, while keeping MBA as an ultrabook.