I also switched permanently from Ubuntu on an X1 Carbon - docked into a 4k screen.
Unit tests and builds run faster, VS Code for both client and server dev is very responsive (3-4 react / python projects open at once with the language servers running), battery life is out of this world - I don't even pack my charger when I'm out on the road all day.
The machine just feels very snappy - even with 20+ apps open, videos playing, 50 or so browser tabs, watchdog running for dev (css, uvicorn). I feel like I spend a lot less time waiting on the machine. No fan spinning and barely any heat.
I really enjoy switching back now to using Microsoft Office and the Adobe Suite instead of the OSS alternatives.
I don't think RAM is like-for-like comparable in terms of capacity, because I see a lot less memory pressure on the 8GB air (I didn't want to wait the 2 weeks for the 16GB delivery) than on my 16GB i7 X1.
The disadvantages come down to architecture compatibility (problems building cryptography and numpy from pypi which was resolved). I offset this by also running a dev server environment on my HP Micro (with ESXi and a bunch of docker machines) over the LAN.
I've since switched my primary desktop to an M1 Mini (16GB) driving 2x 4k screens, and will use the Air for on-the-road work and personal browsing.
I still have the X1 Carbon sitting on my desk - but find myself using it less and less.
The only other disadvantages are number of USB-C ports on the Air - you'll probably want a hub with power pass-through. The display on the air also isn't the brightest - but still comparable to the X1. The pro is better in this regard. Third disadvantage is inability to access high-end GPU if you require one.
There is no real cost argument against the M1 - I don't even know how to spec an equiv X1 Carbon with similar performance, but even customizing the upgrade to a similar WQXGA display and 400 nits takes you to $3k+ (AUD) while the M1 air was $1950 (with 512GB). Leaves you change to get an x86 server to put on the LAN [0].
I'm a huge, huge fan of the M1 and endorse it to everyone I know. It really is a game-changer.
[0] Geekbench for the intel i7 i7-10510U in the X1 shows 992 single core score 3106 multicore, vs 1700 and 7375 for the M1 air. The display is 1440p (vs 1600) and 300 nits vs 400