By your own calculation EROI of Battery buses should be about 15-30 (taking diesel EROI as given as it has no source) if you actually apply the vehicle's efficiency; ~85% efficiency for E2E diesel-generator-to-EV. While diesel bus would be around ~21% effiency.

Source/explainer: https://youtu.be/6c94vRmbM6Y?si=WmCvyB6uKJT7TWZ7&t=444