I think this mostly has to do with the extensive use of vegetables cooked in various tasty ways. Western dishes (specifically West European) seem to have very few good techniques to cook vegetables, leading white children to hate veggies. I think this is exacerbated in Britain and their Anglo-Saxon colonies (cue the meme about British food having no seasoning).

Also, proper Asian dishes tend not to actually use much oil. Stir frying only lightly coats the outside of food with oil, very different from western deep frying.

Anecdotally, I feel less greasy and sludgy after eating fried Sichuan dishes than comparable fried Western dishes.

It depends. Definitely tastier.

Really depends but they do use a ton of oil.