There's a lot of good stuff in this post but you might be jumping to conclusions.
If he had good stuff in his first 4 appearances and bad stuff in his last 6, there could be any number of explanations for that.
He could be sick, his mechanics could be slightly off, he has a minor injury, his confidence is down so he's aiming the ball, etc. All of that could be corrected and the stuff returns.
Or he could be permanently broken, as you said. He is getting up there a bit in age, after all. But there's no way to know that based off 6 appearances.