In my experience, most of them don't. I would be surprised if even 10% of web devs do real performance testing on other hardware (i.e. with actual measurements).
It's not limited to Google either. Try ordering food on a web app on your phone, etc.
For example I just loaded doordash.com in Chrome's mobile view, and it made 110 requests and consists of 7.7 MB of resources. It took 1.12 secs to load on a core i7 desktop connected to a wired network. How long do you think it will take on a phone with a slower CPU over a wireless network? For a web page that shows pictures of food.
FWIW I worked at Google for over a decade, and this was a problem that got worse over the entire decade. People talked about making the network slow to fix this systemic problem, but it never happened (at least while I was there). You also have to test on different networks, although admittedly the M1 doesn't make your network faster so that problem won't be exacerbated.
I still stand by the original statement; the M1 will make the web slower, assuming it's adopted by a bigger fraction of web devs than consumers (which seems very likely).
