I’d say that it should be entirely fine to post to different (relevant) communities. The point of different communities is to let people who may have different tastes choose just the ones that they want.

The problem is that the software doesn’t presently do a great job of presenting these. Like, from a user standpoint, if browsing a list containing posts from multiple communities — be it All or multiple communities that I’m subscribed to — I’d like to see one entry for all of them, with sections for each cross-posted community.

That should really be fixed on the software side, not by users trying to patch around it via modifying their posting behavior.