Regarding the Spit V
It seems to have been an aircraft with a lot of potential, and a lot of bugs to iron out. Early Spit V, VB and VC had several disappointing combat engagements - over the Channel Front against Fw 190s but also against Bf 109Fs; in
Soviet use in the Caucasus in 1943; and at Darwin they were basically defeated. In the MTO from mid 1942 - early 1943 they held their own but suffered heavy casualties and certainly did not dominate the Axis fighters (and they did not face a lot of Fw 190s in that Theater). There may have been numerous specific reasons for this in different Theaters but the engine boost ratings have been mentioned (contingent in part on the availability of high-octane fuel), as has the Vokes filter. There was also apparently a pretty severe problem with gun stoppages with their Hispano cannon. And there was the lingering issue with the carburetor as well.
The effectiveness of the Spit V improved dramatically as gun mountings were changed reducing the rate of stoppages and increasing ammunition, new tropical filters were developed. the use of finger - four / pairs formations was adopted beyond England, boost settings were increased from +9 to +16, and specialized low and high altitude variants were created optimizing performance for different missions. So as has been pointed out in the thread, and early configuration Spitfire V flying at low boost with the Vokes filter, at a maximum of +9 boost and jam prone cannons with 60 rounds per gun, was a very different aircraft from a Spit V flying at +16, with the Aboukir filter (or no filter), and more reliable cannons with 120 rounds per gun.
Regarding the Spit V in Darwin
At Darwin, there were several highly specific reasons for the debacle. First and I think foremost, maintenance and configuration problems. In a nutshell, the aircraft sent to Australia had some major problems flying and fighting especially above 20,000 ft where their performance edge was supposed to be most pronounced. Gun heaters either weren't installed or had been disconnected and guns repeatedly froze. The glycol had not been drained out when the fighters were shipped and there was a major (and largely unknown) problem with the coolant systems being corroded, and the constant speed propellers had major problems as well. If you read about the various engagements at Darwin you'll note that large numbers of Spitfires were being forced to break off due to mechanical problems.
As far as the tactics, the 'big wing' strategy adopted by Caldwell and embraced some of the other DAF Aces was a very hard won lesson from the MTO. In that Theater, Axis fighters, including Bf 109F and G, and Macchi 202s, consistently had an altitude and speed advantage against all the Allied fighters* (including the Spit Vs) so that the only safe way to prevent being repeatedly bounced from above was to form up into large units of 8-12 fighters and turn into all attacks from above, guns blazing, until the enemy fighters either broke off or lost sufficient energy to be engaged. The Zero was supposed to also have an advantage in climb, according to the legends extant at the time, and Caldwell expected similar problems. His skepticism of the American advice was also somewhat understandable as the Americans were still somewhat in a panic about A6M performance and were very much the students rather than the teachers in the MTO.
In reality - in theory - the Spitfires had superior performance at altitude and a higher critical altitude. But with all the mechanical problems above 20,000 ft the Spitfires were struggling up high. Add to this poor coordination of ground support in terms of early warning, weather forecasting and radio beacons, and the Spitfire pilots were really in a bad situation.
Finally at Darwin Caldwell was also contending with an extremely severe problem with their locally manufactured 20mm ammunition. Shells were coming out of the factories of different lengths, with numerous duds, some dangerous (at risk of exploding), and often tainted with sand or dust on them. He was forced to set up a pre-sorting system for cannon shells. This only exascerbated the already severe problems with gun stoppages and specifically at Darwin, freezing guns which took a while to discover and remedy.
Regarding the Spitfire more generally and the Fw 190
Nearly all the problems with the Spit V however were remedied by putting the merlin 60 series engine on it with the Spit IX, and the Spit IX was the solution to the Fw 190 problem. Once you had an aircraft which was just as fast but also vastly more maneuverable, the entire boom and zoom strategy of the 190 was hopelessly outmatched. You couldn't out run it, you couldn't out maneuver it, so what did you do? It was really the older and smaller Bf 109 that bore the burden of keeping up with Allied fighters.
The Spitfire went through many different iterations - for it's time, the Spit I was arguably the best fighter, certainly the best interceptor in the world. The Germans and yes the Japanese as well, proved challenging to the next generation, the Spit V in the early, days of it's deployments (and later deployments of older configurations in remote Theaters). But the Spit IX closed that gap and it never really opened again.
Spit IX, and the longer ranged and more sophisticated VIII, and the XIV etc. which came after, kept the Spitfire ahead of the Axis opposition and, barring jets, capable of enforcing air superiority until the end of the war. So in that sense the Spitfire was superior to the Fw 190.
S
* except for the P-38 - in theory - but they too were suffering from teething problems at altitude
