The Air is only slightly thinner and 0.25 lb lighter than the 13” Pro. I’ve had an Air since 2012 and just compared the two, and got the Pro. There’s essentially no difference in portability. But there are significant differences in capability and price.
I think Apple killed the 12” MacBook because for most people, an iPad is a better ultraportable than a laptop. The folks who are really adamant about laptops with Mac OS are developers, and the MacBook had a bad ratio of cost to power for most devs.
oddly enough, the 12" macbook is the only apple device I was ever interested in. it seemed like a great alternative to an xps 13 if I ever wanted to get into the mac world. lots of devs these days only need a computer capable of running an ssh client. if that's you and you also have a workstation, why not get the thinnest, lightest laptop out there that runs your favorite OS?
I think Apple killed the 12” MacBook because for most people, an iPad is a better ultraportable than a laptop. The folks who are really adamant about laptops with Mac OS are developers, and the MacBook had a bad ratio of cost to power for most devs.