[solardev]

IMO those are different use cases. If that sender or Google itself were to disappear, hopefully the messages would just disappear too. It's better that they become inaccessible rather than public.

Long term archival is a different use case altogether, especially of encrypted materials. It's questionable whether any provider or medium can survive over the long term, so it's better to use an encryption system where you hold the keys and the encrypted data can be migrated to any sort of storage or provider over the years.