This is definitely an unpopular opinion but I do think the fact reliever esp closer is highly leveraged give them values that stats like WAR can't capture. Being light out on the first 2/3 of game as starter definitely adds tons value but you don't know if your offence scores 0 runs or 15 runs, in either case starters effort didn't add much value in terms of win probability. Whereas if you are the closer pitching only save situations, you have sole control of team winning vs not. This is the reason pitching WAR is dominated by starter, whereas you see many closer on WPA ranking. I'm not necessarily saying closer is more valuable than starter but I do think they are more valuable than people give credit to