Even a Seafire is a good energy fighter down low.
I had an La7, a P47 and a spit trying to chase me home from a furball.
Dove for the deck and the spit gave it up and peeled off.
Once the spits out of icon range I reversed back into the other 2 guys. I got a hit on the la's engine leaving him smoking. Merged twice and again, picked my point to exit, dove for the deck and ran. La decided to go home, that left the jug.
Once more the jug slowly caught me, once more at 2k I reversed high, merged with him twice, and then dove out and ran. Left him in the dust 3.5k back and no longer a threat. If I'd had ammo I'd of stayed and killed him. But I was empty and down to minutes of fuel.
I agree that the Yak is VERY good from say 5 - 15k, in decent hands its a constant threat.
Yes the P51 can be flown as an energy fighter, but its poor acceleration leaves it gasping for E after much of a maneuver. Its actually a "downhill" fighter, starts up high, and with careful use of altitude can do very very well.
Once low it needs to exit out clear of the fight and either land or regrab alt.