Yes, I noticed that assumption too, and a few others(for example the assumption of "car parked outside home" - now you have to value either the cost of car ownership and parking, or the time cost for an on-demand fleet to reach the passenger) With a lower speed target the system may still offer benefits over roads and mass transit in terms of reliability/availability. The number of existing PRT companies continuing with this approach suggests it has some merit.

Maglev PRT still seems worth researching for intercity traffic though - the requirements for routing get a lot easier, and you still have benefits of speed and lightness.