I used to be 100% sceptical about supplements, but after suffering with ME for 10 years and having not been given any effective diagnosis of the underlying cause or treatment by my GP, I enlisted the help of a nutritionist.
I was put on a different diet (very different to what the government/NICE etc recommends) and also recommended to take certain supplements.
3 years on and I am fully recovered. Whereas most people I know that have chronic illness (some with ME/CFS) and are still being treated by the NHS are no better but are just about managing their symptoms.
However, to give some balance my nutrionist/clinic does not support long term use of supplements apart from probiotics, Vit D, Vitamin C and EFAs.
I agree that a balanced healthy diet is the key, but there is no guarantee of the nutrient value of that food, given the way food is stored, transported etc. Unless of course you grow your own and only buy food that it is very local. Which is not always prcatical.