Train access or rather lack of is not an issue here, one only has to look at LBA or EMA to see that will not hold an airport back, most people wil either self drive or taxi, over many years the only train I have ever caught to a airport was LHR
I disagree that the 737 is the wrong size for the LoCo model out of DTV baby loads were very good on many routes, but DTV will only support so many routes due to it's location between LBA NCL and a two aircraft base might be viable when gas was cheap but not at current prices.
What DTV need to do is to persuade a few airline to run W pattern flight through DTV thereby avoiding base costs and show there is demand, it may be too late for winter ski but the likes of PRG would be a start.