Injuries almost always have some effect. They just tend to be forgotten over time. And then obviously even if the injury didn't occur, the final result could've been the same.
All sports are moving towards more parity in a lot of ways so it is possible.
Probably will need to wait until after GS run is over. It would be tough for a "pretty good" team to beat them. They would probably need a top-tier team to do their dirty work first.
Heat have no chance to win it all. Sorry and I am a Heat fan. Only a few teams have a chance to win it all. The officiating in the NBA guarantees it. That is why I love the hockey playoffs. Any team can win it all.