This all has little to do with the privacy and security features provided by GrapheneOS. See https://news.ycombinator.com/item?id=45244497 in response to the original post with complaints about Android user profiles, which are not a GrapheneOS feature. Nearly the entirety of the GrapheneOS added features can be used without ever making/using a secondary user. It's not required by sandboxed Google Play at all. Secondary users are useful but not a feature added by GrapheneOS.