Its unfair to say that GS is a bad defensive team. There are games when they loose focus and other teams light them up, but that happens to every team. Watch their defense in crunch time, when they need to get stops. They almost always get the stops they need. That's why they rarely loose close games. They actually had the best close-game record in the league. Watch their first regular season game against Clevaland or their road win against San Antonio. GS doesn't just win high scoring shootouts, they can win ugly, physical games and play excellent defense.
When OKC had them on the hooks, GS put the clamps on them. You say Westbrook and Durant were forcing up bad shots, which is true, but alot of that has to do with GS defense making it difficult for OKC to settle into their offense. And it wasn't just Westbrook and Durant, GS was shutting down the role players who had been killing them in the early part of the series. Guys like Adams, Roberson Waiters, who came up big in OKC's wins, were shut down in Game 7. GS held OKC to under 90 pts in Game 7, which was 20 below their season average.
I agree that these last two games, their defense has been poor, but you also have to remember that they're up against one of the greatest players of all time having maybe the best finals performances ever. I expect GS to bring their A game defensively in Game 7, but with Lebron playing this well, he could still light them up.