Let's look at two seasons from two pitchers shall we?
Player A: 13-9, 2.96 ERA, 140 innings pitched, 31 saves (led league), 60 walks, 114 strikeouts, 4.8 WAR)
Player B: 13-5, 2.17 ERA, 137 innings pitched, 26 saves, 33 walks, 68 strikeouts, 3.7 WAR
Player A is Bill Campbell in 1977. He finished fifth in the Cy Young vote and 10th in the MVP vote. Player B is Sparky Lyle in 1977, when he won the Cy Young Award and was 5th in the MVP vote. My point is that the two pitchers were not really that far apart. Lyle had a better ERA and fewer walks, but Campbell had more saves and quite a few more strikeouts.
Campbell was Boston's first major free agent signing after going 17-5 with 20 saves all in relief for the Twins in 1976. Boston needed a big-time arm out of the bullpen and signed Campbell. His first season was terrific as Campbell was an All Star and won the Rolaids Relief Man of the Year Award. Unfortunately, pitching 317.2 innings in the previous two years took a lot out of his arm and he suffered through injuries for several seasons. Campbell's ERA climbed each year from 1978 through 1980 and he only saved 13 games in those three seasons.
He would never again be a top-flight closer but Campbell was able to transition into more of a setup man. Campbell appeared to be back to being a big contributor in the pen in 1981. He made it into just 30 games and pitched 48.1 innings, but he finished 23 games and notched seven saves, which was actually second on the team to Mark Clear, who had nine. Campbell was 1-1 and his ERA dropped to a respectable 3.17. He also struck out 37 while walking 20, his best ratio in several seasons.
1981 was Campbell's last season in Boston. He signed with the Cubs as a free agent for the 1982 season. He went on to have some decent seasons, but never reached the heights of his 1977 season. He was released by the Expos early in the 1987 season and retired.