Key's offense is not morphing into anything nor was it much worse in this game than it is on average. He did have few ugly dribble turnovers when driving inside which lead to fast breaks... but thats maybe -6 or something like that for his box.
Main reason for Key's -39 was due to the fact that the Clippers kept switching him to Zubac or DJJ and throwing lobs inside. They got a lot of free buckets all game because they forced Key to defend inside, which he cannot do due to his size combined with his poor defensive instincts and lack of defensive hustle. It was clearly something they had scouted and Key was targeted. It does not redeem Key at all, but if we were trying to win Hardy should have also changed things up and bench Key in favor of Juzang or someone who has a chance to get a hand on those passes. I guess he wanted to collect some tape or something.
Also the book is definitely out on Key's transition defense, and there is absolutely no one in the NBA who declines a fast break 1on1 against him. He usually just does the matador defense in those situations anyways.