Thank you so much Dan for your perspective and especially for the effort to make a video! 
I’m relieved to learn that apparently we are not doing fundamentally wrong.
Still I don’t want to give up to get at least a bit more of a system into our campaign structure. I have always understood campaigns in HubSpot to be kind of a bracket around a certain set of marketing endeavours which eventually allows up to report on how an initiative has performed. At the moment, we compare apples and oranges, which is never a good thing if you want to find out the truth. 
However, learning that after many years of HubSpot you haven’t found a perfect set of rules either gives me a certain peace of mind.
Thanks again for your reply, and have a good one! 
Isa