The higher you go, the harder it is to improve. It took me only about 30-60hrs of osu to get used to 4*. For 5*? Well, 5* is gonna be a lot harder than 4* because it is where cross screen jumps, fast burst, deathstreams, etc are getting more common. I have 260hrs of Osu where I always played outside of my comfort zone and I still can't say I am good at it to it. Some 5* like Scarlet Roses and many other 5* maps are so hard that even a good portion of 5 digits (100k-10k) are having trouble getting a good score on it. For 6*, it'll take even longer because it's a whole different level different than 5*. Jumps and sliders are either getting a lot faster, complicated, far apart, or all of them at the same time. Streams are getting faster, longer, and some more space. And you can imagine the rest for 7* and up.
Right now, if you want to improve quickly, ALWAYS PLAY OUTSIDE OF YOUR COMFORT ZONE. Play maps that challenge your limit, but you still have a good chance of passing them. Even if you're uncomfortable playing that one type of map, play it, get used to it, get good at it. Find your own playstyle, don't copy the pros, play with the setting that you're comfortable with. Practice what you are not good at. Always play consistently, don't take a long break just because you feel lazy. Lastly, try to not determine your skill on pp alone, farming pp is fine, but don't go crazy over it, focus on improving yourself than pp, then eventually, you'll set the score you want, I can't tell how many times player (I also made this mistake before, don't repeat it after me) sacrifices the tons of time they could've used to improve themselves for pp that they don't deserve.
