I am experiencing this problem as well. This is a major disaster. I'll properly format for mobile, and the same blocks are way too big on desktop. When I get them right on a 1920x1080 screen, I resize to a medium size window and everything is severely broken again: way oversized.
This has been very embarrassing for me. I would be able to deliver a site much more efficiently abandoning squarespace for hand-coding at this point. SquareSpace, do you have any response to the issues raised in this thread? I need to know if I need to abandon the platform, because this is a total deal-breaker.
