Well, it doesn't have a d-pad, so if you're looking strictly for that, it just doesn't have one.
As far as sidescrolling platformers go, I'm actually a fan of using joysticks over d-pads, so I'm not sure I can really weigh in properly on that question. I think it works fine for that sort of thing personally, but if you like the feel of dpads, it might disagree with you.
As far as Rivals, I just experimented with it a little bit, and it seems pretty promising to me. The abundance of buttons alongside the clickable trackpad means that it's very possible to play the game without moving any of your fingers from one button to the next - it'd just take getting used to. If I were to use the steam controller for RoA and nothing else, I would not use the face buttons at all. I'd use the left joystick for movement, and let the right thumbpad function as a c-stick. The nice thing about this is that you can bind another button to the click of the thumb pad, which I just set to A. That way, swiping on the thumb pad smashes or does aerials, while you can still easily click to do jabs or normals (alongside the left analog), or click to nair. The game initially has four buttons bound to parry, so you can easily rebind at least two of those to whatever you'd like. Then you can rebind the back panel buttons to, say, jump and special, or something, and then you have access to everything in the game without ever moving your fingers.
Uh, don't actually bind back panel to jump, though, unless you want to miss a lot of short hops. It's not actually bad, I think, but it certainly takes getting used to.
