I agree ,and out of the thousands of gigs I have done,I find it difficult to recall bad gigs,.I see nothing wrong with flat fee against 80 per cent whichever the higher ,providing both parties are agreeable,and that the 20 percent allows for the promoters expenses, room hire, etc.
since the definition of a parasite is one who lives on another,perhaps its the performer with the agent who is the parasite.anyway I agree there must be good agents as well as bad.