In Switzerland, we already switched to MediumFast due to congestion in cities. It was a coordinated change and real world tests showed no significant worse mesh performance for most nodes. Meshtastic is evolving fast and I think it does become more and more viable as an off-grid or doomsday communication. It also is hard to censor which could be useful for journalism and free speech. Hence, not a substitute for the internet, but a more and more viable solution for many.

By default it implements rought limits that you cannot exceed to make sure that you do not not transmit too much noise. Additionally, you can always establish private channels for your nodes and / or not retransmit at all.