Wanted to redo 8th to tachyon dans for a while now, but I never did it because I'm lazy, couldn't think of charts and am incompetent.
9th dan is way too easy because of Unorthodox Red (Planned on swapping this with We Fucking Hate You, but too late for that) and Rave 7. The only two hard charts in10th dan is Rose Quartz (this being overwhelmingly difficult as well) and FORBIDDEN. Wanted to redo it to something like: the lost dedicated -> Connect 1986 -> Forgotten -> FORBIDDEN. Luminal is too jack-based. Tachyon is fucking awful.
Anyway, mid-high 9th dan is where improvement rate requires more of a conscious effort than just "grind until I get good at them". You're not hitting a physical skill wall just yet, I'd speculate that the physical ceiling is way higher than that, but it would require some physical maintenance (to prevent yourself from getting muscle atrophy) to keep at a level above low Luminal. You're not at that level yet, don't worry too much about it.
Rhythm games until low luminal dan is almost entirely mental, which means building muscle memory (i.e. processing patterning to hit patterns in a certain way) and improving your reading ability (being able to discern patterns at higher densities).
You're unconsciously building reading techniques already. Chances are, if you're good at rolls, you are trying to find as many rolly patterns as possible in a certain chart to read efficiently. If you're good at jacks, you might notice anchors/longer jacks in handstreams to focus on so it would feel a lot less strenuous to play through. You should find out what you're good at (at your level, skillset specialisation should be prominent enough for you to notice what you're best at) and try to take advantage of that by learning reading techniques to make certain patterns a lot less daunting.
As for building muscle memory, it's mainly about being conscious about what you're learning. Each pattern has their own optimal approach, but these "optimal approaches" depend strongly on the player's strengths and weaknesses. If you're a very strong jack player, focusing on hidden jacks/using muscles that you generally use for wrist jacking is optimal for certain patterning, as they are more developed. If you're a player who's very good at one hand trilling, you try to use muscles that you normally use for one hand trilling. If you're playing wrists up, you're using more than just your fingers; you will be rotating your wrists, which you can take advantage of, which will help substantially for stream speed because it reduces the amount of tension required for certain stream patterns, particularly rolly ones. It goes on and on, but it comes down by being extremely analytic with your gameplay.