Hi Kris,
Just to add to Hannah's excellent response: If you require a lot of your business logic to be in C++, it makes a lot of sense to use the ArcGIS Runtime SDK for Qt. This SDK is specifically designed for this use case, and is very intuitive and rich for C++ developers. AppStudio was not designed for this use case of using C++ as your back end.
Keep an eye on the Quartz release of ArcGIS Runtime SDK for Qt: This will support the development of your UI/UX with QML, allowing the back end business logic to be written in C++. And that will be supported on all platforms: Windows/Linux/Mac/iOS/Android.