Someone did post that. I think they said that the Cubs opponents had a winning percentage of .450 and the Brewers opponents were at .550.
I would caution that this early in the season that difference may not be that significant. A difference of .100 over 30 games is just 3 games. So you’re talking about a record of 16.5-13.5 vs 13.5-16.5. After the teams have played 120 games or more and you are looking at the difficulty of the remaining schedules, a difference like that would be much more significant. A difference of .100 would be a difference of 12 games
Plus, some undeniably good teams are off to so so starts. Even though their records are about the same, I would still say that playing the Rangers is tougher than playing the Mets.
Judging schedule difficulty based just on opponents won loss records also doesn’t factor in home games vs road games. Before this series the Cubs had played 19 away games (including a road trip to San Diego, Seattle, and Arizona) and 13 home games. They were 10-3 in those games, including 5-1 against the Dodgers and Astros.
I think it would be wrong to attribute the Cubs record to an easy schedule. Like the Brewers, they have done well despite some significant adversity.