THIS IS REALLY FRICKIN' DIFFICULT
That's what I hear! I just did some initial work on a more traditional scrolling chart in the practice screen to hopefully make it easier to tell what you have to push and when, and I want to do more (a better indicator of when/how you get things wrong or right, maybe some beat notches along the track). Maybe level data changes after that, Spinning Swing in particular is probably too hard for its current spot.
In case you still care, just wanted to let you know that I just put out the last planned set of "playability" updates, so now on both the practice and execution screens there's a scrolling chart with much better feedback of what you get wrong & right, and there's also a health bar that you can configure to give yourself up to five mistakes per level before it fails you.