I agree with your main points, and I never once thought the Spurs were guaranteed to win this series before it began. I knew it would be a tough, tough series. But once they went up 2-0, it changed things. All the Spurs needed to do was win 1 game out of 2 away. That's it. The shift to OKC changed the whole series, there was no coming back from that.
I think they were good enough to be in the conversation, they were up 2-0 in the WCF. They were supposed to be the veteran team that executed well, but they turned the ball over way too much and that costed them 2 very pivotal games, 3 and 5. Game 3 was a blow out but the Spurs were right there in games 5 and 6, and unfortunately both times the Thunder were able to close.
You are seriously underrating the Spurs when you say they weren't in the conversation, clearly they were, being up 2-0, and being right there in 2 crucial games where the refs and poor decisions were costly.