I think that the original question is not something that can be answered. The reason I say that is because of the dynamics of the teams that each coach had/has during their tenure.
Also, strength of schedule, roster turnover, injuries, assistant coaches, methodology, hell, even the bounce of the football.
So, IMO it cannot be qualified as to who is the better coach because we cannot compare coaches unless they have all the same variables to work with.
Again, I consider a team sport to be dynamic, not static, and many things have to go into account for there to be any reference of who the better coach is.
People say Wade took his teams to the playoffs and better records than Garrett's teams. Well, do we know if Garrett could have taken Wades team to the playoffs? No. Do we know if Wade could have taken Garret's teams to the playoffs? No, we cannot.
So, IMO, the original question is moot.