Hi Werner,
I’m a Rouvy using Xerter as well. I also like the realism of videos progressing at a realistic pace…even if I’m recovering up a slope and hitting 140% downhill!!!
I run a Kikr Core, controlled via Xert on iPhone with Bluetooth. Rouvy is running on aTV. Some how (I know not why or how), Rouvy can take the power reading from the Kikr (using Bluetooth) even when the Kikr is controlled by Xert. The power always matches.
Interestingly this does not work with RGT. I need to have RGT read the power from my Garmin pedals - similar to what you are doing with your Rotor. This means RGT reads a noisier power signal - but the ride summaries and effort stats are always the same.