My guess is that most fast-levelers have pre-knowledge
I have been at this 20 years and never took Kanji seriously until earlier this year. I can pronounce the language but outside of about 100 Kanji that I only knew the definition for, I didn’t know readings with the exception of maybe 15 I learned over a decade ago.
I can barely speak. I can’t really read. I can understand a lot of spoken which I think may be part of the pre-knowledge. When I read the word or hear the reading and it’s something I know, like kiwotsukete (be careful) I just know what it means. This helps mainly on vocab.
So yeah… at first I though no, I am not as fast as I am because I have pre-knowledge but thinking it through, I guess I do OK at this speed because I can understand spoken Japanese at a 4th or 5th grade level. By the time I hit level 20 will I be able to maintain this speed? Maybe not.
The key is the same though for any learner; find something the learner is comfortable with and stick to it. Don’t be a slerched (that’s me) and take 20 years to take Kanji seriously.
Keep at it.
If you become demotivated, stop into the community here and we will help cheer you on, console you, or kick you in the butt to help get you back to learning!
Just don’t give up.