(plus, and this is just a me-problem, I find them impossibly confusing because they ape Facebook's UI, which I find so hard to understand that my one attempt to use it for about a month c. 2010 was nothing but frustration and wondering how the hell normal people manage to use it)
Posts and work groups are actually a generally good way for scalable work communication - and leaving a public and searchable record. This doesn't replace Google docs and wikis, but serve as another layer to organize them. (I promise this doesn't lead to needless bureaucracy, that still happens but not because of Workplace).
If people need you to see something, they can message you directly. I just look at some priority channels semi regularly. No channels create notifications for me, thread replies do not either only DMs and direct @mentions do.