First of all, I trust the manager's judgment more than my own for the reasons that you mentioned. That doesn't change the fact that they have the occasional brainfart and it doesn't take an insider with reams of data to spot those mistakes.
I didn't argue with you about last night. There hasn't been an issue with Kimbrel getting too much work lately and Cora has no way of knowing if a guy will be sharp when he comes into the game. Also, there was plenty of breathing room for Kimbrel even if he wasn't sharp. The problem with Kelly game was that it was obvious that he was blowing up and there wasn't a comfortable lead. He gets paid to know when the guy doesn't have it. He blew that one -- no ifs, but or whats. Of course Kelly is the performer and gets the stain on his record, but no pitcher walks off the mound when they don't have it unless the manager comes to get him. A managers most crucial in game decision is to know when he needs to make a pitching change.