Bullpens are a tricky proposition. You never know what type of season you are going to get from relief pitchers year to year. Look at the example of Edwin Diaz. In 2018 he was the best relief pitcher in the game and couldn’t do anything wrong. Then in 2019 he was horrible and was a major reason why the 2019 New York Mets didn’t make the playoffs and compete for a championship.
I believe that a huge part of a bullpen’s performance is how the manager uses the bullpen and what they do to keep all the relief pitchers busy (not too busy), in rhythm and confident.