Average is not a good measure for that, because there are lots of hours during the day where even the worst ISPs don't have any congestion, and still the connec

Average is not a good measure for that, because there are lots of hours during the day where even the worst ISPs don't have any congestion, and still the connection can be unusable during peak hours. The right measure would be the minimum throughput that you achieved, maybe minus a few minutes of congestion per month that are ignored. If they sell you a 100 Mb/s pipe, that should mean that you should essentially never notice that it's not actually reserved 100 Mb/s. People don't buy 100 Mb/s because they want 100 Mb/s at 3 am, they buy 100 Mb/s because they want 100 Mb/s when they need it, which in most cases is during peak load times (which is why those are the peak load times).