You can paint it yellow, but it's still a really-short bus. That might make sense for very low-density areas, but I was surprised when I needed to hire a school bus for a Scout event last year that the newer full-sized buses actually get pretty amazing mileage. At 10-15 MPG, it's terrible for a car, but when you're carrying 60+ people, that's fantastic. Especially considering you can still buy a pickup truck that gets similar mileage. I was expecting the answer to come back at "7MPG highway" or something more proportional to automotive mileage.
Kudos to the anonymous mechanical engineers who design these things. I suspect it would be really hard to build a full-sized EV bus that used less total fuel, considering the transmission and charging losses, and the fuel equivalence for the additional wealth needed to purchase such a thing.