As I understand it, intent matters a lot, and that is typically through the testimony of people who had access to SBF in an environment where he was comfortable speaking candidly.
Those people are often accomplices. Sometimes the medium large fish get off if they chop up the big fish.
There are the way things should be, and there are the way things are.
SBF was toast with or without Ellison's testimony.
It should be the other way around. You get 10 years. You don't want to cooperate? Great! You get another 10.