I feel there is something that is missing that we don't know about yet with respect to Chauvin. I can't find the article right now, but I read that Chauvin's wife filed for divorce the day before George Floyd was killed. I don't know for a fact that is correct, but if it is, it might go to your theory of there being some messed up perfect storm that made Chauvin turn into such an idiot. And a deadly one at that.
From my own personal experience, I had divorce papers served on my now ex years ago. Suffice it to say, he did far more than what was necessary to lead any reasonably intelligent woman to come to the conclusion that she had no choice but to terminate the marriage. His reaction was extreme anger, to the point of being in a rage. At the time, I was worried some random person might get caught in his crosshairs while he was in his rage. Fortunately, that didn't happen.
I think the blank and disinterested look on Chauvin's face as he kneeled on George Floyd's neck is absolutely bizaare. I think it's bizarre he had his hands in his pockets while he was doing this, and he just looked so incredibly casual and disengaged as he killed George Floyd. As you said, he had a lot of years in under his belt. He could have coasted the rest of his career.
I'm sure we will learn a lot more as time goes on.