I disagree. The 15" MBP is still pretty heavy and big to carry around. At half the thickness, and say 2/3 the weight, it would be a much more reasonable daily driver.
Maybe there should be a 15" MBP lite that is just that?
Also as you said, user replaceable battery, ssd and ram.
Which is why Apple should differentiate between the "air" and the "pro" line more. There would be a place for a 15" air, which is a slightly thinned version of the current 15" pro, and a true pro machine which sacrifices a bit of portability for features and performance. My current dream machine would be roughly like the late 2015 MB Pro (that happens to be the machine I am typing this on), with at least a 16" screen (the bezels are plenty large on mine) and 1-2mm more thickness, allowing for good thermals and more serviceable parts. For a pro machine a battery, keyboard or ssd exchange needs to be doable by a skilled technician on-site.
To me it seems an oddly missing niche. A lot of people spend a lot of time on planes, don’t need much of a laptop, and often don’t much care for tablets as laptop replacements. Nothing really on the market for them.