from my experience playing competitive rhythm game, I'd like to think it like New Game+
you grind clear to expand your skill, once you hit a wall, you go WAY back to practice your accuracy.
once you satisfied with your accuracy stability, you grind clear once again. rinse and repeat.
another trick that I learned is, the higher the difficulty, the higher scroll speed required, which often also includes either re-learning the hitbox or adjusting offset (VERY RISKY, but high reward).
other thing that I might add is skins. choosing a good skins affects your gameplay, but this affects more on outside of 4k. on 4k, just use whatever as long as it doesnt have long "hit animation" that trips you up on dense chart.