In the absence of drag, yes. Once you get close to a plane's level top speed, the heavier it is, the faster it'll keep accelerating past it.
Is it going to decide the fight? Probably, hell, almost certainly not outside of very specific circumstances.
Is it measurable? Absolutely.
E: Also, following your logic, parachuting is impossible.
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Also, saying this isn't true because the 109K outperforms its opponents is a logical fallacy. The plane has in the vicinity of 400 more hp than the Spitfire and Mustang, yet is around 800 kg lighter at TOW than the P-51 and around the same weight as the Spit.