If Rise was random then my family wouldn't likely have gotten it 5 out of 6 tries at 7am and 1/1 the only time I had to try in the afternoon. Back in the early days when you had to be in the park to try and pull of a BG while waiting in a rope drop line, I believe it was somewhat random. These days I'd have hit the button within a second or two of 7am and my wife would have a boarding group before the next page even tried to load for me.
Now it wasn't fair that speed, skill, practice, advance knowledge, etc. made a big difference, but if you followed the procedures it was not hard to achieve at least 50% of the time.