Trungpa was one of the clearest teachers of the Dharma that has ever come to the west. Cutting Through Spiritual Materialism is an excellent work. The only book my teacher ever required me to read. He, my teacher, a Buddhist for over 37 years now, considers Trungpa's teachings to be excellent. I don't think his drinking affected his Dharma. At his level there is no doubt or confusion. Hell, even at my level, which is far from Trungpa's, there isn't much.
I personally know several teachers born in Tibet who have never "sampled the big buffet." But they are monks so they have taken vows not to. On the other side of that coin I have heard stories of many monks who broke their vows in India and Tibet. I don't think coming to the west is much of a factor.