Based on the names of the agencies given in the original post and the salaries/bennies quoted, I would say it's about right. Rishworth is always the lowest in most of what they advertise (I've turned them down TWICE on a fifferent contract because the salary was HALF of what I was currently making and they slashed other stuff by 50%!!).
Parc is usually the best.
If you figure that the client airline pays them a certain amount, then they take their cut and what's left is your "salary". It's quite easy to see with the same contract and the varying rates as to what is going on and who you should be pitching with/for..................
Now, make your choices!