It's trivial to create a luxury "bus" in just about any form factor you want to from a full-size motor coach down to a limo. Presumably the economics don't work in most cases. Of course, if you're talking small municipal airports in the US, the vast majority of people living there, especially those who can afford somewhat upscale transportation, probably own a car.

Yes. Most small towns don't even have bus service to the nearest hub airport, because economically it doesn't work. And there is no arrangement of costs that will work out to electric aircraft being cheaper to own and operate than a bus.

In a sufficiently river/sea/ /hill/valley rich environment it might work if one can save on infrastructure cost for extra expensive roads. This is not most of the world though.

You already have bush planes in places like Alaska. A cheaper/better bush plane has probable merit but, as you say, that's not most places.