I apologise for my ignorance: I've always thought the long cage derailleur was meant to accommodate a huge cassette with a big teeth capacity. In what sense the long cage derailleur cannot be used with a smaller cassette?
I cannot fail noticing your Nytro has a pretty long stem: Isn't is a design option to provide proper Reach?
I know Jeremy you don't expect the answer from me but from Chris

As the Nytro Allroad is based on the Grevil (gravel) frame and has gravel bike tyres, it is just an "equipped" flat handlebar gravel e-bike (you can ride a gravel bike on almost anything except mountain technical singletracks).