I don't totally disagree with what you're saying on the surface but I think you're ignoring the context of each situation. You can say the Heat team was loaded but outside of Wade, Bron, and Bosh who was really there? Most of the players were either really green or they were washed up vets. Look at the 2010-2011 Heat roster:
2010-11 Miami Heat Roster and Stats | Basketball-Reference.com
Then there's the question of team chemistry. Adding a bunch of superstars on one team sounds cool but it wasn't easy for the Heat's big three to effectively play off each other at first. The role players were all mostly unproven too. Compare this to Golden State who just had a phenomal run last year with a squad who already played well off each other, starters and bench included. Durant's skill set meshed so well with how they play he literally just had to slide in Harrison Barnes' spot...not much adjustment had to be made for either party after his signing.