You did allude to this in your video in part. My suggestion would be to use the POK generated by the rarer balls to level up the common balls quicker. It will require greater volume of POK than normal due to the lack of PXP being earnt on the commons, but you will progress quicker. I would then focus when you make those commons into rares is to make them extremely speciallised. Perhaps concentrating on Away and over ball with some on exact, then specialise stickers with over 3 goal difference and maybe high score stickers as an example (The upset or high score catcher balls). That way they will be more usable and will work well in conjuntion with your epics sooner.
There's nothing to win on score rush.. do you know how it's going to work or what's going on Alex? Just watching your video from 6 months ago.. wtf has happened to pooky? And how are you going to move forward?