Over the last two years, covering 287 games and 2,553 innings, the Brewers have posted a 3.69 ERA | 4.25 FIP. That -0.56 margin is the best in MLB with Houston second all the way down at a -0.34 margin. The gap between the Brewers in 1st and Astros in 2nd is the same as the gap between the Astros in 2nd and the Cubs in 10th.
Over those same last two years, the Rockies have posted a 5.61 ERA | 5.06 FIP. That +0.55 margin is the worst in MLB over that stretch by an even larger extent with the Cardinals second to worst with a +0.30 margin.
Now obviously more goes into beating (or not beating) one's FIP than just defense and home ballpark, but the Brewers defense over the last two years has essentially been so good that their pitchers have gotten to pitch their games in the opposite of Coors Field.