Apt sidesteps this problem because Debian-based releases are not rolling releases. Unless you install a custom PPA, if you are running Ubuntu 18.04 and you "apt-get install postgres" you will always get version 10.x. The major version number will not get bumped for Ubuntu 18.04.
If want to use a version of postgres other than 10.x, you can either use a different version of Ubuntu or install a custom PPA.
Apt's target audience is systems administrators. Homebrew's target audience is independent developers who might need to have four different versions of Postgresql installed simultaneously on their laptop, because they maintain Rails/Django/Node apps for four different clients who are each unwilling to upgrade for whatever reason.
IMO homebrew is "messy" because it is trying to solve a harder problem. If there is such a thing as an average enterprise software developer, I would argue that homebrew is trying to solve problems that the enterprise developer does not have.
If want to use a version of postgres other than 10.x, you can either use a different version of Ubuntu or install a custom PPA.
Apt's target audience is systems administrators. Homebrew's target audience is independent developers who might need to have four different versions of Postgresql installed simultaneously on their laptop, because they maintain Rails/Django/Node apps for four different clients who are each unwilling to upgrade for whatever reason.
IMO homebrew is "messy" because it is trying to solve a harder problem. If there is such a thing as an average enterprise software developer, I would argue that homebrew is trying to solve problems that the enterprise developer does not have.