Gambling on losing teams is a legitimate strategy, but more than betting on losing teams I think it is evaluating the risk/reward scenario with a specific bet. Sure, there might be a team that is likely to win, but maybe it pays a penny to the dollar. Basically, winning that bet doesn’t make a difference. I get more entertainment out of betting longshots and making sure the reward is worth the risk.
It if is a underdog, then obviously the pay returns might be very good though, but there are games that the odds might be close though. And just like what the OP has mentioned, Miami Heat was the underdog in every playoff run and yet they won until the finals against the Nuggets.
And so with they apply this strategy, then for sure they will have a good profits betting on the Heat.
But still, it's really hard to look for a live underdog that can go like what the Miami did in their playoff runs.