The percentages detail is very cool, never thought about it! I also think of sin/cos as percentages, but there's one small detail that can be easy to miss. While sine and cosine generate "percentages" between -1 and 1 they don't generate them uniformly, because their derivative is not a linear function! If we were to sample sine or cosine between 0 and PI at uniform intervals we would see that the percentages would "cluster" around the peaks and valleys because that's where the function "decelerates" (or the derivative decreases).

This bit me once!