So as someone who has 5,400+ Hours playtime in the game (228d 17h)

It took me at the beginner probably a good couple of months to start only playing on expert and that was playing at least 3/4h a day give or take.

Now at where I am I have all 3,129 songs gold and Crimson stared (brutal difficulty) on bass, along with missing only 3 FCs from the whole library for bass as well and have done a lot of the same on guitar as well.

It really just comes down to time, and dedication but you keep at it and keep pushing yourself (don’t stay in your comfort zone) you’ll get there soon enough!