The piece is at a relatively rapid tempo, around 120 BPM. I currently finger the chord as 1-2-3-5 and play the fast notes with the pinky finger.
However, I'm struggling to perform this rhythm at speed. Since I need to hold down the lower notes from the chord with my 1-2-3 fingers, I find myself using purely my pinky finger for the repeats, which is quite weak and slow.
One thing I've tried was to rotate my arm and wrist so that the pinky is as low as possible on its key and it helps a bit, but with my thumb on a black key, I have to rotate a fair amount, to a point of some discomfort.
Is there a better way to handle this part?