may be it was necessary to turn his into a side character for the time being so that preeta can get successfully humiliated by karan to the extreme level 😳
That's from a Maker's perspective. Like it was necessary for Karan to turn that evil to pave way for maybe Rishab or to pave way for drama.
While in the story, Rishab has been a disappointment so far. So if your prediction is right then awesome. I don't care who stands against luthras and slap them on their faces with truth as long as someone does that. Because it clearly doesn't look like preeta would anytime soon,she isn't as brave.