It's a different issue, not content.xml. They are aircraft you don't have for which MSFS has decided the closest match is a 747.
Deleting stuff could make it worse...
Dean (DC Designs) once published a free file that would model-map his F15s for people that didn't have them but I think it went wrong eventually.
There are a couple of mapping packages for airlines, don't think there is one for warbirds?