The amount of experience points is pretty irrelevant. He might be calculating the points that way on purpose.
I'd say that unless slower advancement bothers you, to ride it out.
Oh, and in the eyes of most DMs: Wealth and character level are linked. HYaving too much treasure for your level is a huge deal, asking him to give you more treasure in exchange for less xp is like asking him to let you kick him in the sack.