How does anyone know he was a 'meditation master'? He could have just been pissed.
On a charitable view one could imagine that all were pissed and consequently kindly disposed in turn to see Trungpa's words and actions as products of an enlightened being rather than a drunk.
One up for the gin, I rather think.
Or, he's accepted as a meditation master because, well, there is a genuine tradition of texts and practices, and he was trained in that tradition from a very early age, because there is a genuine community of 'knower's who found in Trungpa a genuine master, because, there was, and is, a powerful call in his work to those who have a mind to listen, because, because, because. Not least because his early writing and thinking is wonderfully soulful, and incisive, and present, while his later work, the product of a brain gone soft and spongy under the influence of hard liquor, shows a marked falling away.
The mans misfortune was to come from a highly structured, hierarchical society, in which his place was abundantly clear and constrained, to a world with more freedom than he really knew what to do with: Sixties America, hanging out with Ginsberg et al.
Spiritual mastery and functional skill out in the world, while far from mutually exclusive, are two different skill sets/lines of development.
Speaking of lines, this is a great one...
... "incidentally, a friend of mine's dull older brother told me...