........."Ultimate"?..........No. It's usually cosidered the most advanced form in Goju, so normally it the last you will learn. But there is nothing "ultimate" perse, about it. It, like Sanchin kata, may look fairly simplistic in it's overall appearance (moves wise), but that is just on the surface. You will learn a different aspect (level of understanding) about the principals and their applications from studying this form.
All streams flow to the sea because it is lower than they are. Humility gives it its power.