I would say “not always”. There might be an instance where the package is built against Revit 2019 that has a node that uses new APIs like, shortest path tool. If user attempted to load that same package in Revit 2018 the error would have been totally valid since that node will not work, and its caused by the Revit API dlls.
In any which case, I think users should pay attention to these warnings and be aware of what they mean rather than conditioning them to just ignore it. Agree?