The thing was unusable on my lap. After 30 minutes or so just coding, it would get so hot I had to put something between it and my legs. My partner could hear the fans from the next room. And to cap it off, since Big Sur I've been unable to get more than 4 hours off the battery—usually more like 3.
Compare that to the Air: I'm losing two USB ports which is annoying, the speakers are nowhere near as good, I miss the bigger screen, and I'm down 16GB RAM (although in retrospect, I never needed 32GB for my workloads anyway). But in return, I get almost no heat, zero noise, nuts performance (my test suites run 2x faster on average, despite running on two fewer cores), and so far 10-12 hours off a charge easy. And I get real function keys instead of the Touch Bar.
Happiest I've been with a computer in a long long time.