I can tell you that the vast majority of F/Os, and I am speaking of business aviation where I have spent so far all of my career, operating for Austrian or German AOCs are making FAR less money than the people refuelling their planes, and this is not an hyperbole, it is an actual fact. And I believe they do not have to pay the rating for the truck they drive, unlike pilots.
Look it up on PPJN or visit the GA forum if you do not believe me.
Many skippers are not much better off.