While that's true, they also demolished the league's best teams this year on numerous occasions. They made what everyone thought was the 2nd best team in basketball in the Spurs look bad multiple times. They completely outclassed them. So I don't buy that what's happening now is necessarily a product of them facing real competition for the first time.
I do think OKC deserves credit because as you said, they've got elite talent themselves and they are playing the best basketball they've played since 2012. But there are other underlying issues with Golden State like cockiness and bad habits. It's like the Chip Kelly offense -- it's cool to use 4 seconds on the playclock when you're moving the ball up and down the field, but when you keep going 3 and out and your defense is exhausted by halftime, then that style of play isn't going to work.
That's essentially what's happening to GS. OKC have gotten in their head and it's affecting their play. Because they've been so successful playing that way for the better part of 2 years, it's what they resort to even when logic says they need to slow things down. It basically comes down whether they can change up their game enough to get back into things, and whether they can do in such a short amount of time.