I think it's fair to say that as long as two of Joey Ortiz, David Hamilton, and Luis Rengifo are consistently in the lineup, the Cubs will have the overall advantage at the plate. Brewers do have a path to somewhat negating this imo with their high end upside if Chourio and Turang can sustain their current level of performance, which the metrics suggest they can to a significant degree.
Defense is basically a wash between the two clubs as both are elite by DRS. Though, PCA in CF probably gives the Cubs a slight advantage as none of the Brewers OFers are at that level.
Where the Brewers make up ground right now is their pitching, especially their starting pitching, where the Cubs are absolutely decimated due to injury. Brewers pitchers miss way more bats than the Cubs to begin with.
I don't know why anyone wouldn't think at this stage of the season it won't end up being a battle to the end between these two clubs. Exactly the way it's been the last three years, with the onus on the Cubs to unseat the three time defending champions. Both should be playoff teams regardless.