I kind of think it would almost be better if Robby weren't Johnny's son. Not to eliminate his character, but make his story his own and not tie him to Johnny. They make such a big deal about Miguel's relationship with Johnny, to the point that the fan base was screaming for justice for Miguel when Johnny said he loved Robby. Johnny and Robby also don't really have a lot of meaningful interactions, especially in seasons 3 and 4. At this point, it seems like Robby's character is being used more as a plot device to maneuver Johnny's relationship with Miguel than anything else. Johnny is portrayed as such a bad father to Robby that having Robby be his son makes it hard to root for him as a character. If Robby weren't Johnny's son, his story would be a pretty straightforward, heartwarming redemption arc of him getting his life together. But the fact that he's supposedly making all these strides toward being a better person through teaching karate, being a dad figure to Miguel and dating Carmen when he is so incapable of caring for or about his own child really throws a wrench into that development.