And a share of gross revenue, at that. I'm sure all these definitions are written in the studio's favour. Apparently, Stan Lee never got anything for his creations either (and Spiderman grossed $800M+).
'off the top' means revenues, not profits. Profit sharing opens you up to all kinds of creative accounting reducing the profits (or even turning them into a loss) to the point where you're not getting anything.
That's why they say: "profit points are for suckers".