Well, I don't know if this helps, but let me share some info about myself: I have almost double of your playtime and I never passed any +6* i'm working on my consistency rather than going fast, even if sometimes I just want to try passing really difficult maps. if you want to see my taiko history, you can go to
my site and see my taiko posts in the "other stuff" area. There you'll see a lot of stuff about how I felt during this last 10 months of daily taiko gameplay.
About your improvement on the game, I think it is just the "play the game" thing, but let's get deeper into it.
First of all, let's just be sure that you understand this like me: playing for 5 years is different from having a playtime of 200 hours, it is really important to understand this, because in the first case, you can have someone like me, that plays mania for longer than taiko but is clearly better at taiko than mania.
Second, I think ADHD and Anxiety can influence your gameplay, but your potential to get THAT play isn't affected. In other words, you can sometimes get your head lost in the middle of the map, or be nervous to get a really amazing score, but at the end, it is something that is exercisable for sure.
Directly answering your questions: You'll be the #1 in the world just if you play the game trying to improve and if you be confident about your skills. Don't compare yourself to others about PP, ranks and other stuff. Compare to understand (logically) what you should get better at: do you need to get better accuracy (lower unstable rate)? do you need to get better at maps with more difficult patterns? do you need to become more consistent?
Those questions are hard to understand and be 100% sure that you are in the right path. BUT, don't forget that every time you miss something, and you are willing to get better or learn from it, you will notice that and by noticing you need to think on how will you get better or hit those notes in the right way.
The last thing that may have crossed your mind when you say "I wanna be same as Japan players". They are REALLY good, yeah they are. BUT there are a lot of people that came from other taiko games, that's why they don't have much playtime. And there is this thing that taiko is really popular in Japan when compared to Brazil, for example, so people learn really early about how to play taiko, in the first place.
Last but not least, by watching your replay, I feel like you could try learning how to alt. I have a friend that plays 5.2* maps with DT (getting 99% accuracy) and singletaps everything! Taiko is a gamemode that has a lot of crazy people for sure! And, no, you're not a "noob" player. I'm jealous about you being able to play that density and get that 5,89* pass!
This is a long read, I know, but sometimes I feel this just like you and tons of other people, because everything here is normal, everyone has their path. And explaining this to you actually helps me!
Thanks for your attention and keep it up!!