But would Dornish tactics actually work as well for say, the Reach or the Stormlands, in Doran’s ideal invasion scenario? Didn’t the Dornish rely on the Red Mountains for cover/escape, and have to abandon all of their castles? (And also Dorne already being described as already mostly dry/barren–and with a smaller population to support–and thereby possibly less vulnerable to scorched earth dragon fire tactics, and a sense of us vs them nationhood holding the insurgency together).

Arguably better. Guerrilla fighting is generally easier in more populated areas, because you can hide more easily and get support from more of the population (to quote Chairman Mao, which I rarely do, “the guerrilla must move amongst the people as a fish swims in the sea.” Easier to do that when you have more sea to hide your fish in). Likewise, Dorne’s barren geography means that there’s a limited area to hide in vs. the thousands and thousands of square miles you could potentially hide in across the rest of Westeros; on the flip side, Dany’s armies would have to occupy much much more territory, dividing them more thinly, and her dragons would be even harder pressed trying to fire-fight the whole of the continent. And finally, Dorne was conducting a guerrilla war with a far smaller number of fighters. 

To give a relevant example, look how effectively Beric Dondarrion and the Brotherhood Without Banners conducted a guerrilla war with less than 200 men in a relatively confined region. Now imagine dozens if not hundreds of Beric Dondarrions with many more men, better trained and equipped, in every corner of Westeros.