> this just seems like a gamble rather than the well-reasoned short position based on deep (and unpopular) analysis that his subprime mortgage play was.

A short is a gamble all the time because you don't know the time component. Burry was "lucky" in that it happened fast enough. There are lots of people who want to short Tesla but don't dare to because of the cost involved in it and unpredictability of when their bet would pay off.