I understand the thinking behind that, but I don't think it's quite that simple.
In modern baseball you need it all - position players, starting pitchers and relievers.
As far as individual players go, sure, a reliever can never be as valuable, because they only log 60-70 innings.
If you think market prices have any meaning, the most a reliever can make is about half of a starter (Chapman vs. Cole, for example).
But there's a value in having an elite closer which is not necessarily measurable. The Red Sox might have won the World Series in 1975, 1986 and 2003 if they had a great closer those years. And Foulke, Papelbon and Koji were huge factors in 2004, 2007 and 2013.