That is partially true, but it doesnt apply to other Miami-based sport franchises so its not the entire truth.
Also another franchise with something similar to Heat culture is the Patriots, and while Boston is a big city its not the jetset destination for the ages, the weather isnt great and afaik their income taxes arent competitive with Miami either. The Steelers and Ravens also share a similar culture of grit and toughness, even if they have less Super Bowl appearances and wins to show for it (being in the same conference with the Patriots and the Chiefs being the biggest reason probably).
Both Heat and Patriots have in common the fact that they bring in a lot of undrafted guys who turn successful. I think the main key about both of those cultures is that they prefer guys who have a huge chip on their shoulder for whatever reason, and who are therefore more driven to work hard and more dedicated to winning. But it all starts from the top. The coaches (Spo, Belichick, Harbaugh, Tomlin), owners and GMs are all 100% dedicated to the culture.
What you are right about is that playing and living in some of the super depressing cities is a massive hill to climb for those franchises.... which is why its great we own both Minnesota and Cleveland drafts over the next 5-6 years.