The point I made was about the tiny cars makers are forced into when they are trying to get hi mileage without electric assist. Those gas/diesel only cars end up with tiny cabins and gas mower engines. They do not serve the needs of very many people.
A 2012 Prius is a Hybrid and gets 50 MPG combined. A BMW 1 Series 28i gets 33. That's not "slightly less". An Active Hybrid 3 gets 33. Ditto
The diesel infrastructure is there principally for long haulers and construction. Having cars on diesel is piggy backing on it. If you flood the general population with more TDIs then more pumps have to be build or gas ones converted to diesel. Scaling diesel up doesn't come for free. It all adds up to wasting resources chasing something that won't go the distance.