In my opinion, removing free features from OSS software is always a symptom of bad C-level decisions. Everyone understands that it will destroy the community, because it kills the trust. Usually, making things like that is a last attempt to keep the product alive, to avoid layoffs, etc. It seems that Mattermost is not healthy for the last few years. Mattermost have started removing features at V10, and completely killed the community in V11. Will the next versions will go further, and introduce more limitations, like 10 users max for one server, etc?
It’s a common mistake of management to prioritize tactical measures, instead of strategic relationships, under the pressure of problems with money. Unfortunately, it usually makes the situation even worse in the long run. Most of Mattermost’s adoption comes from the OSS community, which makes free promotion of Mattermost to SMB and Enterprise. Also current pricing is not competitive with MS Teams offering for SMB. As far as I understand, MM has a priority to work with big enterprise customers now, but current decisions will vanish community users. Have you estimated an SMB option, like a 100 USD yearly license to remove all ad banners, limitations, etc.? Providing predictable costs is crucial for SMBs and communities (because per-user pricing always has some amount of fluctuations), and SSO is crucial for EU users (which is a legal requirement now to use Mattermost in schools, for example).