I have some numbers to back this up, and at some point I will pull them together and present them. But the short version is:
Because the NL Central has 3 of the 5 worst teams in the NL in terms of both record and runs allowed, the Brewers have had significantly more games against these 5 generous teams than anyone else (including the Cardinals who have more of their games against these teams still on the schedule) So, the Brewers have had more opportunities to face the league’s worst pitching staffs, and that pads their run totals relative to other playoff contenders.
On top of that, the last time I looked at this, which was just a few days ago, the Brewers were averaging about 2 runs per game more against that group of 5 worst teams than they were against everyone else. That difference is significantly greater than any of the other contenders except for the Mets, who just score more than the Brewers in general and have had better pitching too.
So, at least IMHO, the perception that the Brewers offense is worse relative to the rest of the league than indicated by the raw R/G numbers is valid.
The fact that the pitching has not been elite just makes things worse. Last night’s game is a prime example. Last year, and even earlier this year, the Brewers might have won that game 1-0. Peralta goes 6, Boxberger, Williams, and Hader each pitch a shutout inning, and it’s a win. There have been a lot of games like that lost in the last few weeks because the offense isn’t putting up enough runs and the pitching is less reliable than last year.