If you are taking his advice to heart, then there is absolutely no reason to be arguing about his advice not working at different BPMs >_>
The only time when accuracy becomes becomes muscle memory is when you have extremely long streams when the music is a blur (as in you can't really hear the beat very clearly). Other than that, by learning the slower tempo streams you begin to develop a sort of mental clock that keeps track of the beat along with music. Also looking at new combos is a very helpful way to know where you are in relation to the beat. I would just look at the new combo and the distance away from it I am, and adjust accordingly to be able to reach that note at the correct time. Sometimes the combo is really long and so it gets a little harder (and it becomes muscle memory for you cursor moving hand, but you are still able to hear the beat and stream with accuracy if not your cursor be accurate).
Also, I have learned this lesson many times when playing piano. Going fast first isn't going to help. Doing so results in very unstable and insecure playing. You tend to mess up randomly a lot more. But if you practice slowly first and get that very solid and exact, speeding up the tempo to the current on will not be hard and it will greatly increase stability of my piano playing. Sadly, I still don't give enough of a shit sometimes and still do it anyways. And I'm not some mediocre piano player saying this, not to be arrogant or anything, so I have a lot of experience in such things.
tl;dr Playing fast stuff all the time will result in muscle memory accuracy, which will make it hard to be accurate in other BPMs. Playing slow stuff will mentally develop a clock that will aid your accuracy through conscious thought, not muscle memory, which will be able to adapt to other BPMs.
The only time when accuracy becomes becomes muscle memory is when you have extremely long streams when the music is a blur (as in you can't really hear the beat very clearly). Other than that, by learning the slower tempo streams you begin to develop a sort of mental clock that keeps track of the beat along with music. Also looking at new combos is a very helpful way to know where you are in relation to the beat. I would just look at the new combo and the distance away from it I am, and adjust accordingly to be able to reach that note at the correct time. Sometimes the combo is really long and so it gets a little harder (and it becomes muscle memory for you cursor moving hand, but you are still able to hear the beat and stream with accuracy if not your cursor be accurate).
Also, I have learned this lesson many times when playing piano. Going fast first isn't going to help. Doing so results in very unstable and insecure playing. You tend to mess up randomly a lot more. But if you practice slowly first and get that very solid and exact, speeding up the tempo to the current on will not be hard and it will greatly increase stability of my piano playing. Sadly, I still don't give enough of a shit sometimes and still do it anyways. And I'm not some mediocre piano player saying this, not to be arrogant or anything, so I have a lot of experience in such things.
tl;dr Playing fast stuff all the time will result in muscle memory accuracy, which will make it hard to be accurate in other BPMs. Playing slow stuff will mentally develop a clock that will aid your accuracy through conscious thought, not muscle memory, which will be able to adapt to other BPMs.