What we tend to forget is that courses have to cater for the lowest common denominator.
Speaking purely for Type 1s here, when you consider that 56% of patients in the last National Diabetes Audit had an Hba1C between 7.5% and 10%, 27.3% were below 7.5%, only 7.5% were below 6.5% and 17% were more than 10%, then there is a greater requirement for courses to address the 73% rather than the 27.3%, given the DCCT complications indicators.
The whole point of the courses is to improve life for the far less engaged than those who are actively participating on the internet/in local groups. There are some 150,000 members of this forum, of which 15,000 should be T1 if the demographics of the forum match the population. The majority of those are reading rather than engaging. Based on the NDA data, there is no way that all of these watchers have an Hba1C in target. That's why the courses exist.
It's a much cheaper way to at least attempt to get everybody on track with better management of their diabetes. It's got an evidence base that demonstrates that it works (and one that shows better results than the evidence base for either pumps or CGM systems, which is admittedly a little sparse).
For those of us who have worked out how to manage our diabetes using principles that are essentially the same as DAFNE teaches, and have been doing it for years, then yes, they aren't a great deal of benefit. For those who struggle or are new to the condition, they can be life changing. The key addition they need is to introduce experienced practitioners of the principles they espouse and get those on the courses involved in the network of community support.
Whilst I've spoken mainly about T1s there, the reality is that the same applies for T2s.