I've done a lot of ACS assessments and some manage fine and some struggle, depends on the person and what they do for a living, a lot of people just install boilers now and are rubbish at flue faults, vents and controls, but there are a lot of people out there who are simply not working to a high enough standard, they simply want to make money and don't take enough interest to do things properly on a day to day basis, they can't purge, calculate RPGs runs, have no concept of proper pipework design etc etc, they struggle and a lot get referred as they can't get through the exams in a reasonable time, and these are the ones who say the system is rubbish haha, it's easier to blame the system than their poor work standards