So Ryuki is what Kamen Rider is to you? Nothing wrong with that, but I don't think that's really what Kamen Rider as a whole is about, and it looks like Urobuchi might not understand that either.
Well, apart from being biased due to growing up with Ryuki, I do believe Ryuki wasn't such a big step away from the typical Rider format people think it is.
In the original Kamen Rider, Hongo Takeshi and Ichimonji Hayato were the only cyborgs to fight for justice because they escaped the brain-washing process. The rest of the cyborg soldiers were built the same, trained the same etc. That makes them pretty much just like the Kamen Riders themselves right?
The thing about (almost) every Kamen Rider series is that the source of origin for both the heroes and villains are the same, it is just up to the user to decide whether to fight for justice or chaos.
I feel Kamen Rider Ryuki just attacked this concept differently. Instead of Riders JUST fighting monsters created by a central villain or organization, they fight each other. All of the Riders in the series gain their powers from a single source, who isn't quite a good guy. They then decide whether or not to use their powers for their own ambitions or fun (Gai, Ouja, pretty much every rider in Ryuki) or to actually use it to save others (Ryuki, Raia).
And with this we get a lot of drama and dilemmas but the theme is clearly there - Using power to fight for humanity or using it for "evil". Having antagonist Riders in Ryuki was pretty much the equivalent to villains of the week. Instead of monsters, we have Riders, and I believe Urobuchi is saying that despite the title of "Rider", they are the equivalent of monsters.
This is something that hasn't been done since Ryuki, since every Rider battle afterwards has been because of misunderstandings or the evil Rider is actually a monster (or they are just dicks like Kaixa). I feel like Urobuchi wants to try the Ryuki approach again by making the Riders the equivalent of the actual monsters.