They run those tests with like 1Mb/s connection though.

Good point - by default Google Lighthouse is aiming at the 85th percentile of mobile connection speed, meaning you can ignore these metrics because you have a faster connection or device, but they are still true for ~15% of your mobile traffic. That's the reality of simply delaying scripts - you'll want to delay them more to achieve faster loading time, but the more you delay them the more data you lose.