Dalton...
Excuse me but that is hogwash. The Spitfire was the superior plane when compared with its rival Bf109 at almost any point in the war after 1941. There is very little comparison data vs. the G-10 because the G-10 came into the war so late. Figures I have are that it didn't enter signficant service until after October 1944 - by then the Allies owned the skies. The Spitfire XIV entered the war about a year earlier.
If you take a look at
Spitfire Mk XIV versus Me 109 G/K - A Performance Comparison, every reasonable effort is made to make a fair comparsion between the two rivals.
Furthermore, a lot of the performance of the Bf109G-10 (and the G-14 and K) are gained through use of "Special Emergency Power", which was not really that valuable for combat operations. Use of the GM1 (NO2) system required the right load and rpm conditions and MW50 also be available. For most reasonable combat comparisons MW50 boosted performance but not GM1 should be considered.
Also, as I've mentioned before, the Bf109's had very limited top speed performance - the cooling system simply didn't work very well at high speeds because of the boundary layer seperation issues. Messershmitt chose to accept this limitation rather than suffer the increased drag and weight of increasing the scoop size, radiator size, and coolant capacity. The British on the otherhand, made the other choice, enlarging the cooling system and scoop mouths to try to injest the turbulent air and get what cooling could be had from it and increasing the available power to overcome the drag/weight penalties. Neither solution was optimal, but the German solution was more limiting.
Also, generally speaking the Spitfire had more effective firepower from about the Spit V on, and with the Spit XIV it also had a much superior gunsight. And Spitfire pilot enjoyed much better visability than the 109 pilot from about the Spit V on. The pilots ability to see the enemy first is a huge advantage.
In general the Bf109 simply was not as adaptable as the Spitfire. It was at its peak with the F model, after that it was increasingly obsolete.
http://www.faqs.org/docs/air/avbf1091.html gives a lot of detail on the Bf109.
In General though, I'd say both the Bf109 and the Spitfire shared the same basic flaw - both were very much limited to the interception role. They could only be used offensively with the saftey of overwhelming ground superiority, so they could operate from fields very near the front lines. You don't win wars by relying on interceptors.
The FW's were much more competitive, but also lacked range. Furthermore, the FW190A's lacked high-altitude performance, a critical weakness, and both the P-51 and P-47 were more than a match for them anyway. So few D's and Ta's saw combat as to have made little difference one way or another.
=S=
Lunatic