The German losses in the Battle of Britain weren’t that traumatic; they just made invasion impractical. They still had air power in Africa, France, and the USSR for years. They had plenty of planes and pilots, but they were planes designed for war on the European continent - few long-range planes, few heavy bombers. Once the USSR moved its manufacturing east of the Urals, Germany had no way to stop the production that eventually overwhelmed them in the USSR.
What destroyed their ability to defend their cities from Allied bombers was the later ability of American fighters to fly all the way to the targets (using newer planes with drop tanks and such). Until we did that, they were inflicting heavy casualties on our bombers.
The Germans never developed a four-engine bomber.