You're forgetting some of the features of PI.
It is the only of two zones blue side where you arrive by ferry.
There was no annoying train making noise as it went by.
It felt like the "Big Kid" playground, you're finally a 5th grader, you can play with the sixth graders now.
Plus, it is a small "land area" zone with a simple layout.
Steel-Kings-Skyway, to me, all felt a lot a like.
Of those three, Steel is my favorite, no question.
And PI is not my favorite zone, but compared to Steel, I would go with PI.
Oh, by the way, I'm not the final say on any of these battles, so feel free to call me a marshmallow head, just not to my face, or to my circle and triangles.