Project colossus is low volume,and the truth is im not used to such low volume training..
That is because most trainees go into the gym and try to do "too much volume", or don't train to a proper RPE for Failure.
Where in fact if they are faced with a high intensity set their true RPE on the all-out set is around 7-8 with plenty of reps in the tank.
If you observe most people who say they hit failure, they still have at least 2-3 true reps in the tank. People are hitting "Mental Failure" before "PHYSICAL Failure". You will most likely need a partner to push you there so you get an understanding before you run the program according to plan.
It's not about doing more and more sets for volume (law of diminishing returns) Intensity sets are made to be lower volume for a reason. You would be surprised at how taxing PC Is, especially if you run it according to plan and match the RPE's week in and week out.