Good points! I'd like to learn more about how bullpen overuse is measured, because there's IP obviously, but I feel like the truest definition of bullpen overuse is how much pitching talent a manager is not able to put on the field in a given situation/ game/ span of games, so maybe weighting IP by ERA+ or 'how many players are in the red' (using the Jays stoplight system) might be better. There are probably papers on this, but I'm too tired to read them right now