Yep, you nailed it. The stronger that joint is, the less floppy the outside end of your collar bone will feel. I completely detached my ac joint in 09 and have struggled to keep that area healthy, along with my spine injury. Three years ago I started losing tons of weight and the shoulder went downhill fast. I started doing timed planks back then, eventually working up to push ups. I can’t go all the way up without major grinding, so they’re 3/4 push ups….I started with three sets of 10

Now, several years later, I’m up to three sets of 90 every day….with a goal of three x 100. My shoulder still gives me issues, but much less so. And my back issues have improved somewhat, but won’t get better completely.
moral of the story…..get that joint as healthy as possible….