Rider VS Rider is nothing new.
In V3, his own friend was turned into a monster and he had to kill him. I saw that as a Rider vs Rider, just like how Kabuto had to kill Scorpio Worm.
I liked Riderman vs V3, no matter how short that was, because like all kids, we just want to know who's more powerful, and in what ways.
Rider vs Rider is a big turn on for kids who are just looking for excitement when they get to see their favorites clash with all their best.
It's like watching Goku vs Vegeta.
Besides, Gen said it depends on the user on how they use the power, and I think the reason why they're calling it "Armored Rider Gaim", and then there's the "Beat Riders", they're really going out of their way to try and not call it Kamen Rider in the show. It's almost as if they're just waiting to build up to see which one of these "Riders" is truly worthy enough to be called a Kamen Rider IN the show.