You're not comparing against real-world fixed-route bus routes.

In the real world, most bus routes run nearly empty if not completely empty most of the time, belching diesel smoke and paying a driver, in order to ensure that service is provided to remote locations and that service is made available on a regular schedule. In cities, utilization is usually higher, although you see the same pattern off-peak.

In suburban and rural environments, the footprint is nearly irrelevant, but the lack of riders means that early attempts would start with designs that prioritize battery capacity and range over the sheer number of seats. In urban environments, the final mix of buses will look closer to a combination of mid-size buses for door-to-door and full-size buses for trips that are door-to-door but in practice are no different from fixed-routes due to the sheer number of people who take the current routes at rush hour.