I suspect Genta isn't in that posedown because instead of partaking in that fight, he's off doing something that involves Takeru's storyline. Genta has no hereditary clan duty to whoever the official Shinken Red is, after all. He's just in this because of a childhood promise to Takeru.
I'm not surprised some folks are not feeling excited to see Kaoru and instead are sympathizing with the idea of Takeru effectively "losing his job." I suspect that's how the story wants you to feel, since Takeru's the guy we've seen as Shinken Red for 42+ episodes.
If we aren't attached to him by this point, at least a little, then the story has failed. I might ever feel the same way if I wasn't pretty sure that Takeru will be back as co-Shinken Red, at the very least, before the series is over. Until then, I'm going to have fun with Shinkenger's writers getting their historic first on.