As many have said, there is more than one way to skin the cat so to speak. There are examples of good and just OK defenses that have won titles. Usually the champion is at least pretty good in both but perhaps most importantly, had at least one really good "shot maker".
I know shot maker is not a measurable distinction but it refers to guys like Paul Pierce or Kobe or Wade or Dirk. San Antonio never had single elite shot maker but between Parker, Duncan, and Manu, they always had options.
Golden State has perhaps the best shot maker I have ever seen play in Stephan Curry. No one has figured out how to stop him these last few years. They have other good offensive players that play off him and they have good enough defensive personnel to play sufficient team defense.
This is a really good team we are watching with a really good player on a really good run. They have to beat a very different Cleveland team this time though. LeBron is more than adequate as the "shot maker" and the team depth for CLE is there this time. It will come down to JR Smith, Love, and Irving hitting the shots they need to hit more than second tier Warriors. CLE should win in my opinion but I would not bet on this one. (I thought OKC would win so shows you what I know).