Try this. When you're doing the daily missions, there are some that give you blue orbs (idk what they're called). Well, those missions scale with the level you're currently on, also you dont have to claim the reward before starting a new mission so id recommend finish all the missions that give blue orbs and push as far as you can, when you decide to reset(it'd be best at a boss stage cuz usually those are the ones that hold u back) first claim all ur daily missions and then reset before the boss stage is over because if you go back to xxx5 the rewards will scale back to that stage. Also use affection to unlock all the powers in the bottom right corner.
Just for reference, I'm free2play with no gacha girls and I'm pushing 6k after about 2 weeks of play