IMO the problem stems from a dreadful choice of candidates. There appeared to be no worthy winners or at least no winners amongst those that could cook. They all seemed to have major faults that no amount of training could eradicate.
The issues seem to be:
Why did he not just be brave and say that none were worthy of opening a restaurant with. (no mention was made of opening a cocktail bar)
Why did he pick the winners as being 2 people who already had a successful central London business as a cocktail bar which also served food to share. Not only was JJ unable to cook but he also showed little inclination to learn!
The Winkers were an established business not two contestants striving to get their first restaurant!
In almost every programme the Winkers were shown to be inept (albeit as were many of the others) but at least the others cooked and followed the given brief!
In the final Chris delivered all the required courses including using vegetables from the garden and coping with an hours delay to the start of the meal. Nathan was Chris' downfall.
JJ ordered in veg, burnt the veg for the stock, made a lumpy glue for the risotto, the petit fours were not petit!), and made soup instead of a souffle! Where was Blackadder when JJ said 'I have a Plan'! Totally stage managed!
It all looked wrong! and it felt wrong to most viewers. I cannot believe that they did not sit down and watch the programmes and see what impression would be given to the viewer with all the inconsistencies throughout.
Blanc just destroyed his own credibility