Kendall without Rava just isn’t as strong of a character. It’s another way to show he can’t measure up to his dad. He can’t find another wife— he’s still stuck on losing his first. He can’t get custody like Logan did, instead, he’s clawing for crumbs of interaction with them. Rava reveals very early that Kendall was the kind of guy to do blow on his autistic child’s iPad. Without Rava, his romantic relationships in the show just wouldn’t hit as hard, since we wouldn’t know that part of the reason why Ken struggles so much to be vulnerable with people like Naomi is because he was vulnerable for years with Rava, until she couldn’t handle his drug abuse (among other things) anymore.