Bf109K-4 (ENY 20) or P-47M (ENY 10), Spitfire Mk XIV (ENY 5, 10 Perk Points) and Ta152H-1 (ENY 10).
The Bf109K-4 is at least competitive with the other three fighters and in some cases is superior. All four fighters are functionally air-to-air interceptors only. Either the Bf109K-4's ENY is too low or the other three fighter's ENYs are too high.
Agreed. The 30mm is hard to aim but gives a one-hit kill capability that no other fighter armament has. It has the speed and firepower to murder bombers in slashing attacks like few other prop planes in the game. I'd give the K4 a 5 based on flight characteristics and killing power but bump it to 10 for the bad ballistics and bad views. It's not easy to learn but with a skilled pilot and its fantastic vertical performance nothing with an ENY worse than 15 or so can touch it in its element.
Bf109F-4 (ENY 35) or Spitfire Mk V (ENY 25).
The Bf109F-4's usage and K/D are higher than the Spitfire Mk V (per Lusche's charts) and it has significantly higher performance. The guns favor the Spitfire Mk V, but it has a short ammo clip of only 6 seconds compared to more than 15 seconds for the Bf109F-4's single 20mm cannon. Both are functionally air-to-air only. Either the Spitfire Mk V's ENY is too high or the Bf109F-4's ENY is too low.
I hadn't flown either all that much until recently, but after flying these planes almost solely against each other extensively on both sides in the Malta scenario and TDIH I would take the Spit V all day against the 109F-4. More ammo doesn't help you if you get killed before you can use it up, and the F-4's combination of one 20mm plus two useless popguns makes it much, much harder to get kills unless you can saddle up on somebody and shoot them up for a good long while. It seems to me that anything less than two 20mms or 6 .50s crosses a critical threshold when it comes to snap shots. And the Spit V is superior in just about every respect at higher altitudes.
Ki-84-Ia (ENY 20).
The Ki-84 is a very capable, all round fighter. It has decent firepower, range, agility, speed, durability and bomb load. It seems, based purely on performance, that its ENY is too low.
Agreed in general, but, while it's great in a low furball, it has one severe limitation in the MA: unless you're low and slow anything Allied or German can just dive away and laugh as the Ki starts shedding parts. I'd put it at no more than 15 for that reason.
In general, it seems to me that just about every German plane in the game should be bumped up by about 5 (10 for the K-4 which is a killing machine). The Fw-190D-9 is a dominant fighter in many environments, a decent pilot can slaughter slower turny birds with impunity all day in it with a little patience and SA. It should be no worse than 10. As you noted, the Ju-88 is better than a Betty in every respect and while it's light on bomb load it has an unmatched ship-killing capability with torpedoes.
I suspect the Luftwaffe birds are docked for having steep learning curves, but with a skilled pilot who's past the early part of that curve their capability is much higher than their ENYs suggest. If anything I'd say planes like that which are difficult for newbies to fly but murderous in the hands of vets should be hit
harder by ENY because the vets are the people who need limiting the most when they have a numbers advantage - a horde of noobs are just more cannon fodder no matter what plane they're flying, but a bunch of aces in 109K-4s
and with superior numbers are death on a stick.