This is a little silly. Kurfurst just has an affinity for the German aircraft. It's not about Red vs. Blue. I haven't seen anything posted on his website that's questionable, although admittedly I haven't read it
all.
At any rate, I think he would be the first to say that aircraft performance in game should be affected in a very limited manner, if at all, by accounts like these. Performance should be dictated by viable sources, ie manufacturer's documents, and replicated as best as possible in game.
Comparisons do little to give hard numbers. There is no way for anyone to reproduce every time the results in either one of those tests. We aren't provided with enough information on atmospheric conditions, engine settings in all regimes, and on top of that, the aircraft aren't being flown by the pilots that have trained to fly and fight in them. As an example, most 109 pilots knew about the aileron snatching. Personally, I wouldn't have tried to turn that tight unless I was evading, or just being overzealous in trying to get a kill. It isn't an indication of the Spitfire being completely superior to the 109 or vice versa.
In fact, the problem with these comparisons is that they fuel the idea that, even if by all accounts it's said that these aircraft were evenly matched, well then surely the (insert your aircraft here) was still 5 or 10 kmh faster, could turn tighter, and climb 200-700 fpm faster. That's just the way it was.
Evenly matched also doesn't mean that they had the exact same numbers in every category. It only means that they were close in most categories, and in the ones that were different, it took the skill of the pilot to exploit these advantages to their fullest, and not let himself be drawn to expose his machine's own weaknesses.