Yes. I have seen that. This is why I call it a grab bag. “Edit in Wavelab” is about precise, microscopic editing to an individual audio event. That is about as far away from mastering as you can get, IMHO. In my opinion, the idealized workflow is defect correction → mixing → mastering. If you have a mix problem while mastering, you are already in trouble. If you have an audio defect to fix while you are mixing, you are already in trouble.
In the real world, we do what we have to do, so I’m not saying it is a bad thing to have the ability to quickly go back and fix the source audio if you overlooked something before you started mixing – or somebody gave you bad WAVs. But it ain’t mastering in my book.
The kind of integration I would like to see is in the real mastering process. If you mix a stem, then you should be able to click one button that puts you into the mastering environment with that stem open and ready to go. The files should all be saved within the overall project folder and so on. And if in the mastering process you discover the mix wasn’t quite right, you should be able to click one button and return to the open mixing project just as it was before you created the stem. Maybe this is possible with Wavelab and Cubase. If it is, it isn’t obvious to me.