Here's the difference between the Heat LeBron joined and the Warriors Kevin Durant joined.

Stop putting Steve Kerr's Warriors pre-Durant and Eric Spolstra's heat pre-LeBron together. They're not similar.

Heat's last 3 seasons before LeBron James
15-67 (no playoffs)
43-39 (1st round exit)
47-35 (1st round exit)

Warrior's last 3 seasons before Kevin Durant
51-31 (1st round exit)
67-15 (won championship)
73-9 (lost in 7 game finals)


Heat's league MVPs LeBron joined up with: (none)

Warrior's league MVPs Durant joined up with: 2x defending MVP Steph Curry.

Miami Heat's odds of winning it all before LeBron joined them: 50/1.  

Warrior's odds of winning it all before Durant joined them: 7/4. 

Conclusion

These teams are not comparable. The Warriors are/were already being discussed as an all-time great team. Curry is/was already being discussed as the best player in the league. The Heat were never close to being the best team before LeBron. Wade was never even close to being considered the best player in the league. The Heat hadn't been to the finals for 4 seasons, including a 15-67 season where they finished 15th in the East. The Warriors are a young team that have dominated the West for two straight years, The Warriors had years left of dominance in them without Durant. If Durant gets a season ending injury, the Warriors are still the favorites to win it all. When LeBron left the Heat, the replaced him with Luol Deng and Goran Dragic and Hassan Whiteside and still missed the playoffs that next year.