I did the same exercise earlier for 2019 —the best WAR year for Barnes. Go figure. You want to cherry pick 2017-2019, his best WAR years? fine. His average WAR is around 1.1 through these years. i.e. He is at the boundaries where FG calls you Role and Solid player in the re-scaled charts for relievers, and that label certainly does not make you good by any means. I know what average is, see? lol
As I said, only few RPs are in-between Solid and MVP levels. Barnes is not in that category if you take his WAR career numbers before 2021. He is nothing but a role player. Below average if you want to feel better lol
Again, I know what average is, but it is not explicitly shown at FG's chart, so you have to look where you can locate those RPs who are labeled "average" RPs in the rescaled chart. As I said, the Solid level could be a fair translation.
Thing and the root of the problem is, that you don't like how I rescaled the chart which is not rocket science if you take 3.5+ WAR as the new MVP level for relievers which is a fair number in my book. I still not sure why. You still can do it, regardless FG does not have one.
Again, if you want to keep rating RPs in the traditional way; i.e. in a 3-level chart (good, average and bad), it will be very primitive and flawed because Mo and few others can't be at the same tier and among of a lot of mediocre and below average (role/scrub) relievers like Matt Barnes.