I dont find the idea of a immutable "descriptive" tag or branch to be that useful (I also dont find the differentiation of tags and branches to be useful either) I've seen plenty of repositories where tags end up being pretty ambiguous compared to each other or where "release-20xx" does not actually point to the official 20xx release. Immutable references are more typically handled by builders and lockfiles to which Git already has a superior immutable reference system, the commit hash.
I 100% agree on the latter (the tag != release is more of a project management issue), and the same concept applies to containers and their digest hashes. The main issue at the end of the day is the human one: most people don't like looking at hashes, nor do they provide context of progression. I would say "give both" and make sure they match on the end user side of things, but tags are the most common way (open source) software releases are denoted.