First, thanks for linking a page with autoplaying video, LOVE THAT.
Second: combat aircraft are about much, much more than speed. Note this line: "...The reigning air speed record of the time was 469mph, set by a German Messerschmitt plane in 1939...." That was the plane that LOST the Battle of Britain, by the way.
The Bf109 was 10% faster than the Spitfire during the Battle of Britain anyway, an even faster plane - assuming it would remain so, after the addition of reasonable fuel tanks, armor, guns, ammunition, and a fighting canopy - would have helped how?
Note, the power/weight ratio for this racing plane, 3.44 lbs/hp, is precisely the same (curious?) as the unloaded combat Spitfire. Wing loading is much less, but if we presume the addition of 1000+ lbs of combat-necessary weight, that would be rather worse.
No, this is a clever design, a very pretty bird, and will be interesting to see fly. I would be a little nervous, without seeing the wind-tunnel results, of flat spins and yaw control generally, not to mention forward-swept wings being notoriously twitchy in practice.