I don't think anyone would disagree that the Brewers rotation that now includes Woodruff and Miley is better than the Cubs rotation, but the question might be whether that difference is enough to overcome the fact that the Cubs offense is quite a bit better than the Brewers. The Cubs rotation might not hold up, but time is running short for them to fall apart.
The Brewers winning percentage depends a lot more on how many runs they score than who the starting pitcher is. To illustrate, the Brewers are only 15-13 in Burnes' starts. Their winning percentages are better in games started by Houser (11-6) , Peralta (16-10) Rea (12-8), and Miley (11-8). Those are all in a fairly narrow range given the number of games.
The run support per 27 innings for the entire game started by these pitchers clearly explains a lot of this: Peralta 5.2, Houser 5.1, Rea 4.8, Burnes 4.3, Miley 3.9. The worst example of lack of run support is Teheran. The Brewers are 3-8 in his starts despite 5 quality starts, largely because of run support of 2.8 runs per game.
I'm not going to say that who is starting doesn't matter, but as shown by the feast (5 runs or more) or famine (2 runs or less) offense the Brewers have displayed the last 3 weeks. the main question for me before each game is not "who is starting?" but "Can the Brewers score at least 4 runs?''