The Yak-3s have been a common sight for me, curiously though they usually seem to be accompanied by a spit of some kind. I've been able to sucker quite a few Yak-3s into a 1v1. A P-38 can't match roll but can beat it just about everywhere else. A P-40 has little chance unless it's flown by a skilled pilot (clearly I'm not the right man for the job). A P-47 can give them a good run for their money if the jug driver is patient and waits for the Yak to go vertical. A pony is a Yak's worst enemy. It can outperform the Yak on every level, and in my case I was able to fight off a second Yak with it while testing (only got the kill for the one though).
Explain to us how a P-51 "can outperform the Yak on every level".
The P-51 is faster, as long as it has WEP. Without WEP, not much difference. Especially at low level. The Yak-3 has a turning radius much, much smaller than a P-51. It climbs much faster. It accelerates much faster. Co-E, Co-alt, equal pilots, the P-51 has two choices... Avoid a fight or die. Ditto for the Yak-9U. P-51s have 5 minutes of WEP. Conversely, the Yaks have, essentially, 25 minutes of WEP. You are making the most common error I see. You assume because you beat a guy flying something, it was because you had the better fighter. I've beat Spit16s and La-7s with a P-40... All it proved was the suckiness of those pilots. The P-40 is a pig, but a pig was more than enough for those guys.
Here's an example. Take a P-38J/L and a Ki-84. Equal pilots, meeting in a classic duel. All things equal at the start. The P-38 is toast. The Yak is very much like the Ki-84, in that it does everything related to dogfighting better than the P-38. Now consider that the Yak-3 is faster than the Ki-84 (and the P-38), turns better and climbs like a rocket.
Tonight, I shot down three P-38s with a Yak-3. Easy work. However, those guys weren't very good. Even if they were, the P-38 has no advantage to exploit. I chased down and killed a Yak-3 too.
Trust me when I say that you don't want to meet a good stick flying a Yak-3. Your P-38, P-47 and P-51 are ill equipped to burn off E trying to get a shot. The Yak will slice and dice them with similar efficiency to a Spit16. You pick your American iron. You encounter a Yak-3 at your altitude, and you merge. Should you reverse off of the merge, the Yak will whip around and be pulling lead long before you've fully reversed. You will be on the defensive immediately.
Any time you may want to test your theory, shoot me a PM and we'll go to a quiet field in the TA and you can have a go at it.