Billy Wagner 853 games in his career with 903 innings with 422 career saves. The 903 innings doesn’t seem like a lot only 100 complete games if you look at it like that. So how can this guy be the 202nd player of all time. Well relief aces are a different position and the innings they pitch are more critical. I know both the WAR and Win Shares formulas make an adjustment for pitching critical innings.
Win Shares does it on all save innings. I am not sure how WAR does it, but the 9th inning is crucial in the formula. If they wanted to get more exact they could rate them on easy, medium, and hard saves. There was a book in the 90s that defined the three saves and rated relief pitchers on how well they did on all saves. Baseball Reference does track all innings pitched for all pitchers (and at bats for hitters) to figure out Win Probability Added. This could become part of the calculation for WAR especially for relief pitchers. With so few innings they have to be treated differently especially relief pitchers.
I don’t think anyone had problem with Mariano Rivera being elected unanimously to the hall of fame. However, all three formulas don’t give a lot of credit to relief aces since they pitch so few innings. I included additional information, so I have Rivera as the 20th greatest player of all time. That seems reasonable for being the greatest relief pitcher of all time. Joe Posnanski has him in 91st place and probably had to move him up to do that. I think I am closer on Rivera’s impact on the game with him and other relievers. This is probably the only area in baseball I would say something like that with Joe Posnanski. He is a great writer and has a great knowledge of baseball. I highly recommend his books and anything else he writes.