I checked from my end, and the CSS provided by David isn’t affecting anything in the Blog and Archive Pages. What does it look like from your end? Can you take a screenshot?
I have checked it again. If I look at the archives in the customizer, then they look weird as I wrote. Outside the customizer it looks okay. Why is that?
No, it’s just we need to iron out some of the theme styles for when content templates are used.
However, with the GPP 2.2 there is a new Loop Template Block Element, which will allow you to create the entire loop with the GB Query Loop. This method will allow you style the columns/grid in the editor and avoid these kinds of issue with the Theme styles