Basically the risk would be someone like TikTok dropping out of the store, but I find that unlikely. Maybe at the best they will have an "unrestricted" version with bonus features outside the app store. Visibility for indie apps is basically zero on the big platforms, but for the large players, being in the app store is actually important, at least for now, as users are used to going to the app store to search for software, and not just typing something into google.
The other thing is, these apps will still be sandboxed. Being available outside the store just means they can accept their own payments, they aren't going to have full system access to photos/contacts/files/etc. without explicit user permission, same as an app available via the app store.