In terms of simple single-seat fighters there was no magic in designing a decent fighter IF you had a competitive engine. Stick to basics, keep it simple. You do need to know who you are going to fight and when the war will start. A year out and you have a MS406 when you need a D.520."
But mainly there's no point in getting deep into technical things if the doctrine isn't right. The RAF was not prepared for war. The Air Staff had the intelligence form Spain but did not use it, preferring to stick to their delusions.
I think the problem here is that this thread exists because we all believe and know that "things could have been different i.e. better if...", so much of this thread is gonna revolve around hindsight. The statement above is valid, but to a point. How many of the world's air forces at the time, apart from the Germans, DID heed the lessons from Spain? Approximately none, in reality. Not the Americans, perhaps, but not overly certain the Russians did, the Italians certainly didn't, or at least the lessons they took away from Spain were the wrong ones and we know the French were too busy in-fighting to notice... The RAF had lots of problems going into the war and with hindsight we know what these were - turret fighters? Blenheims and Battles flying straight and level over heavily defended targets? Army co-operation with the wrong aircraft? The problem is, what was everyone else doing that was so much more on-point? The Airacuda, anyone? The Zerstorer? The Breda 88? Everything French?
You see, by the standards we apply, before the war
everyone was in a bit of a quandary about how to fight wars, not just the RAF. I bet if we spend time scrutinising every other major air force in the world, we'll see lots of discrepancies, it's just the RAF gets so much more attention because of its position at the time. It was one of the biggest, most powerful and most modern air forces in the world and
compared to what is the point I'm making. The USA might have had shiny all-metal bombers, but only a handful of real useful ones that were entirely unfit for modern combat and their fighters were not a match for European ones, the French were too busy arguing and undermining each other, the Italians were still swanning around in biplanes suffering from delusions of grandeur and like the Germans converting transports into bombers with odd characteristics, the Russians had some modern aircraft but were stuck in the perpetual hell that living under Stalin presented and were still largely agricultural in most things and no one at the time believed the Japanese could do anything worthwhile, meanwhile they were, but with their own inter-departmental rivalries and lack of forward thinking that hampered their future plans.
The Germans were organisationally and in some ways equipment-wise the best at what they did - extensive reconnaissance assets and infrastructure - no one else, not even the RAF was as well equipped, one of the best fighters in the world in the Bf 109, some good but odd bombers with performance (the Do 17) that was nothing to shout about, but equipped with the most modern means of finding and attacking ground targets - the Knickebein and X-Gerat devices, which made them potentially the most accurate bombing force in the world. With some really good operational level commanders, no one else compared. What was the downside? No follow through and bad leadership at the top. Talk about bad or inadequate policies for war? What happened to the Bomber A and B programmes? Converting everything that flies and carries a bomb into a dive bomber? The rampant inter departmental in-fighting and currying favour that was actively encouraged by the head of the Reich, for starters?
The thing is, if we look back at what the RAF was and balk and cry out in shame, we have to then put that up against the lessons it learned when the chips were down. Bomber Command got its big bombers, its radio navigation aids, (let's not forget the US 8th AF originally wanted to fly daylight missions WITHOUT escort fighters in 1942) Fighter Command got its 400 mph fighters and had in the Spitfire one of the best performing and longest serving fighters of the war, Coastal Command met the U boat threat with technological advances despite starting with barely adequate collection of motley machines resembling Dastardly and Muttley's Flying Circus. And what about Army co-operation? Under the stewardship of Coningham, the RAF Tactical Air Forces set the benchmark for close support, pioneering the hallmarks of the artform we know of today. And what about the jewel in its crown, the Empire Air Training Scheme? There was nothing else like it. Lessons learned and overcome, with help from reliable and resource abundant allies. Communication was the key to victory - the RAF employed people from all over the world and worked well with its friends to get the best out of its assets. The enemy didn't play well with others, certainly not as well as it could or should have.
Look at the Germans, by comparison. They got some pretty special stuff done but failed at the fundamentals. Supply, logistics and strategic planning for the future all went out the window. The Bomber A and B programmes were beyond their reach, forcing them to retain elderly inadequate aircraft for longer than anticipated, their jet and rocket programmes were stifled by shortages thanks to the extensive Allied bombing, their advanced engines, while innovative and clever were failing on the work bench - essentially they bit off more than they could chew - that's bad strategy for you.