You can make this argument all you want about "rattled" Ottavino. But his FIP was right there with his 2019 numbers, and he had a higher K/9 and lower BB/9 than in 2019.
It's not about "ignoring" that one outing that resulted in a loss as it is keeping it in context. He threw in 22 games, and in 20 of them allowed 1 ER or less. He actually has a good shortened season that looks a lot worse because of one bad outing that might have come on a day when maybe he did not feel well, or was distracted, or just was a little sore. That stuff happens. And when you pitch in 60-70 games, a day or two like that gets more easily absorbed into the rest of the season.
Now if you want the downside of the 2020 Ottavino as compared to the 2019 version, his FBv was down almost 1 mph. (This might not mean a thing, as a lot of pitchers around the league had similar issues, likely due to on/off ST). His Contact % was up. His Swinging Strikes were down. And in both years, his FIP was in he 3.40-3.55 range, while his ERA's were 1.90 and 5.89.
Still, he is not some "rattled pitcher" who needed to be dumped. He is a good pitcher who will probably settle into the mean of those two seasons, and that means he will largely pitch effectively. He was a good add for the Red Sox and right now represents a loss for the Yankees, although they are more prepared to absorb it, and presumably did so with other moves in mind. But if you think someone like Loasigia is going to merely step in and fill his void, you best hope it is not a very big void...