So your implying the additional win on the win curve is worth a top 15 prospect (Torres and Frazier) or multiple top 30's (Boston's package for Kimbrel)?
I do think you are working with a biased sample here. Essentially you are saying any team that's a playoff contender is a World Series contender (I agree), but effectively any team that's above average is a playoff contender, thereby is also a world series contender. I think it's generally understood that closers don't provide value to below average teams. So you can basically justify any price paid for a relief pitcher as a premium a contender must pay to win a world series.
We are 10 years deep into teams paying above WAR values for relief pitchers. The market is clearly stating what the perceived value of elite relief pitching is.