I don't think we are missing the point, we were looking for a Slack alternative and found one. They charged a bit to give you push notifications, now they charge more of it. If not having push notifications were an option for us, we'd have simply downgraded.
Then you also need to build and distribute Android and iOS apps for your employees. Congrats, you now have a significantly larger project than "put Mattermost on a server and update it occasionally".
I am using it on both cloud-hosted (work) and self-hosted (friends chat) servers.
Push notifications work fine, the mattermost app that's already on the android and iOS stores work fine, they have done for the 3-4 years I've been using it.