Yea there are many factors at play here. One of the most important factors is how far does the system reach. Frequency isn’t as big of a deal if we are talking about a much bigger system. For example, I’m sure many would be ok with a 15 min frequency time if they could hop a train in Mississauga that brought them to Union.Those types of maps need some modifier to show actual usefulness (service frequencies or seats per hour at various times of day). Metro running trains evening trains every 20 minutes (pink line) and every 5 minutes (Red Line) are very different experiences for the rider despite being presented the same on most maps. We find the same with commuter service where peak-only lines like Milton often have the same presentation as UPX with all-day 15 minute frequencies.
Anyone making such maps can find the shape files for North America here (see "Download Data" link) https://www.thetransportpolitic.com/transitexplorer/#11/43.6251/-79.4239
So I took a look at the system lengths.
Chicago 165 KM (overnight service)
So we have to look at the numbers with context which seems to be what you’re doing but not others.