Honestly, I don’t think ENY is nearly as bad as people make it out to be—at least until you start getting above about 20 ENY.
I think a lot of the complaining really starts when people lose access to the 5 ENY aircraft. Those are the planes people are comfortable in, and when they're suddenly unavailable, it feels like they've been forced into something terrible. But between 5 and 20 ENY, there are still plenty of very good options.
Take the P-51B, for example. At around 20 ENY, it's still a very capable airplane. I think the biggest reason more people don't fly it is simply the armament. The performance is there, but a lot of players don't like giving up the heavier guns.
The P-47 lineup is probably one of the best examples of ENY not being a huge problem. There are good Thunderbolt options across a wide range of ENY levels.
The P-38 is also surprisingly ENY-proof. The P-38J at 20 ENY is, in practical terms, almost as good as the 12 ENY P-38L probably 99% of the time. And even the 30 ENY P-38G can be a lot of fun if you keep it extremely light.
Once you get into the 30 ENY range, though, things definitely change. You can still fly effectively, but you have to work harder. The aircraft generally become slower, less forgiving, and less capable of controlling the engagement.
On its own, I don't actually think that's a problem. Having to fly less capable aircraft when your country has a numbers advantage is a reasonable mechanic.
The real problem is what happens at the same time.
Your country has the numbers advantage, so you're restricted to worse aircraft—but you're also often fighting on multiple fronts and getting gangbanged anyway. So you have the population advantage on paper, but that doesn't necessarily mean you personally have an advantage where you're actually fighting.
That's where the ENY system starts producing frustrating gameplay.
You end up with situations where the only available fight is trying to launch a 30 ENY aircraft while a group of guys in 5 ENY Ponies is orbiting over the field waiting to kill anything that takes off.
Sure, you can up from an uncontested base and fly over instead of repeatedly getting vulched. But now you're flying a slower, lower-performance airplane and spending more time just trying to reach the fight.
And look, I'm absolutely in favor of upping a mediocre airplane against a vulching horde and seeing what you can do with it. Sometimes that's one of the most satisfying things in the game.
But that's the difference: doing it occasionally because you chose the challenge is fun. Being forced to do it repeatedly because ENY has taken away your viable options while the enemy is sitting over your field in their best aircraft is where it stops being fun.
That's the part of the current system that bothers me. It's not simply, “I can't fly my favorite plane.” It's that the combination of high ENY restrictions, bad local fights, and enemy hordes can leave you in a situation where you're simultaneously supposed to be the side with the numbers advantage and the guy trying to take off in a 30 ENY airplane against 5 ENY fighters already positioned above your runway.
On paper, that makes sense as balancing.
In practice, sometimes it just means the side with more players gets punished globally while individual players still get slaughtered locally.