Hmmm, an interesting proposition. In fact, primary soloists and featured players may have a claim, and, in many orchestras, do make more money. I don't know about the arrangements in German orchestras, though. But not your average section player. But that extra money would be based more on the featured aspect as opposed to the number of notes.
How about the cost of the instrument, relative to others in the same family? A world class Stradivarius, Amati, or Guarneri violin can easily fetch over $1,000,000, while its viola or cello counterpart may be worth "only" $150,000 or so. Maybe viewed as a "return on investment", there may be a basis. But then, any klutz with a million bucks and no talent could buy a Strad. That doesn't make him or her any good. And looking at time in training, education and practice, well, it's pretty much even, right across the orchestra.
Personally, I think the cowbell player ought to get the bigger slice. After all, a violinist doing a Paganini exercise can flub a note, but it goes by so fast you don't notice. The cowbell player has ONE note in a whole symphony and if he puts it in the wrong place, BOY, that's a clunker!