> Even if you take it to be only 3x and compare per passenger-hour rather than per passenger-mile, which nobody ever does

But driver-hours (definitely not passenger-hours) are the correct metric if you're considering biking as a substitute for driving. People take longer trips in cars than they do on bikes because they can. If the mode of transportation shifts, trips to the store won't get longer to adjust -- the stores will become more dense to accommodate the reality that people need closer stores.