I bought a macbook air in ~2012 and it was unusably slow after a year. bought a thinkpad to put linux on after that that I'm still using today (although admittedly it's a bit of a wreck now - still, it lasted for 8 years)
The MacBook Air was not really a "high performance" machine to start with though - you can't compare that with a ThinkPad :)
And it was seldomly updated, so you could get very aged specs.
If you bought a MacBook 2011/2012 you would typically get an HDD and between 4 and 8GB RAM. Software requirements/demands sky-rocketed shortly after that. On a non-Air you could at least upgrade this yourself, which gave the machine new life ("just like new")
it did have a 128gb ssd. The thinkpad was also an x1 carbon (also 4gb of ram), so it had a similar form factor, not sure about cpu specs, I probably should have mentioned that.
Interesting, I wonder why mine slowed down so much then. From what I remember it was after an OS upgrade, it was my first time trying a mac, and I ended up being disappointed and going back to linux, but I also didn't do a deep dive into figuring out the reasons for it.
I believe the 2011 era MacBook Air (EveryMac.com confirms only the 11”) had an entry level 2GB RAM variant. That one probably got pretty painful after just a couple OS updates.