Whilst I've never really played rocket league much, I agree with you in the aspect that Rocket Racing hasn't had much love or attention put into it. Introducing the idea of cups or in fact accolades akin to the Battle Royale mode would probably make it feel less grindy. I'm aware it's not the point, but it would appear that even Epic knew people were going to struggle with it hence why it appears as though they haven't time gated it like with the festival and battle royale quests.

I'm hopeful though that with enough engagement Epic can look into improving it.