Johnson's version of history is the golden gloss, written from the victor's point of view. It tends to skate over the hardship and exhaustion, terror and overwhelming odds, and how close Britain came to losing in so many ways; starvation, lack of man-power, lack of equipment, lack of almost everything except courage and the will to survive at all costs. He does mention how they had to rethink their tactics, and eventually adopted the Germans' well tried and practiced methods learnt in the Spanish war. Also he talks of how much he learned when flying with Douglas Bader, right up to when Bader disappeared from the sky.
He was lucky in that he missed much of the Battle of Britain when the majority of British fighter pilots were being shot down mainly because of their inexperience and inadequate tactics, in the same way as Clostermann escaped that particular carnage. He was also lucky in sticking with the evolving Spitfire; while Clostermann went on to fly a wide assortment of aircraft on different kinds of mission, some of which he survived only because he also had the Top Gun prescience. Both were frequently moved by their instincts, ahead of time, only to see bullets streaking through where they would otherwise have been.
If one reads both of Johnson's and Clostermann's books, then I think it is possible to gain a much better balanced view of how the second war was fought in the air. Each is rivetting in their own way: Johnson sailing over the problems is more reminiscent of Biggles; while Clostermann gives us the grime and warts, the fear and the death, and the politics and confusion. Both were flying before the war, both struggled to get into the action, both survived the war, each gained an incredible number of victories, but their two stories are so different, making two different sides of the same coin.
I think Clostermann's is the better history, based on his diaries and journals, better written, more realistic and with more background, but Johnson's is the more exciting and pacier to read.