Actually he is right. In only two weeks during the entire battle of Britain did the Luftwaffe succeed in destroying more planes than the RAF replaced. They needed to do that for six months in order to destroy the RAF, but they wouldn't have survived it for six weeks. The RAF started the battle with 600 and actually gained more planes as the battle went on; British plane production was moving far faster than the Germans were shooting them down.
On July 6 the RAF had 1,259 Pilots, and on 2 November they had 1,796. By comparison, between August to December in 1940 the Germans lost nearly a third of their fighters and a quarter of their bombers. The Germans were in fact badly losing the battle of Britian; they were hemorrhaging pilots and plains faster than they could replace them (Adolf Gallad, famed German pilot, even at point apparently said the Luftwaffe never recovered from Britian; it had lost too many experienced crews and pilots), so the decision to switch to city bombing wasn't a mistake. It was a desperate attempt to salvage a strategic victory from what had otherwise been a complete failure. It worked kind of, Luftwaffe casualties slowed down because escorting single big raids was easier than a bunch of little ones, but in the end Luftwaffe never really came close to beating the RAF.
Could they have, possibly? Maybe, but too much would have had to change for the Germans for it to be realistic.