Open forum to everyone else's best practices, but in general I have the same approach and general annoyance with what you're describing. For the bulk of our production apps I follow the same approach you have in that staging is a copy of the production app and all development done in Prod or approved from Staging must be duplicated/reworked in the other application. I almost never use the out of the box sandbox that QB provides given the lock that it places on Prod and the short term / all or nothing nature of the environment.
Our implementation process is to develop everything in staging first so the two environments stay in sync and have minimal deviation and then port to production once approved and validated.
To my knowledge there is no way to truly do a prod/staging/sandbox setup in the classical IT way of thinking about it.
Typically our sandbox/development environments live for 3-6 months so while its a headache, I've found that being diligent about keeping the two environments in sync allows that timeline to extend, but this is a core feature that needs some focus for larger/more controlled enterprises.
