I can only go from my past experience of really struggling, and it was because my technique was bad. I had done so much endurance that I could go at 12k or 13k quite easily, and could sustain that speed, but I couldn't get into "Pulse" mode. My muscles had learned to make circles, and I couldn't stop it.
I know I didn't get to 13.5k that quickly from when I first started Powerballing, (though I put that down partly to the fact the "Community" wasn't very large then, and I didn't have the motivation. But for over a year I couldn't get near 13.5k again. 13.2k was about my limit.
The only way I saw of improving was to change the direction I rotate my wrist. Yes, at first it was dire, and my scores dropped to around 10k. I didn't do 100% reverse-rotation, but I did quite a bit. Slowly my scores improved, and the more I tried it the quicker they improved.
One day the technique started to click. My record was 13069, and in a single session I did something like 13.5k, then 13.7k. Next session I did 13.9k then 14k. Ever since then my scors have continued to rise nicely.
I still spin in my old, original direction when I first start a Powerball, and also if I'm sitting and idly spinning away gently. Plus I can get near 14k in my old direction these days too, (though I've not tried for a long time).
Perhaps a radical change like this might be what you need?