These were all great characters who were dropped into strong stories, but perhaps part of their success could be attributed to the fact that World War II was still a fairly recent event when they were created. Or perhaps it was because that war was one of the few in history in which true evil was confronted and soundly defeated.
World War I was longer ago and it ended with the a "peace" treaty that did nothing more than create conditions for eventually starting another war. So comic book writers and artists looked to that war less often for heroes.
There were a few tries, though. DC was very successful with Enemy Ace, the first series to tell a war story from a German point-of-view to an American audience. DC also had the Balloon Buster, an American pilot, but he didn't enjoy the success that Hans Von Hammer did.
He was a fairly minor drop in the comic book bucket, though he did have a few more appearances during the Silver and Bronze Ages. One particular issue of the Hulk, in fact, shows us that the Phantom Eagle played an important role in the history of Marvel Earth.
Hulk #135 (January 1971--written by Roy Thomas & penciled by Herb Trimpe) involves Kang the Conqueror in yet another attempt to manipulate time and conquer the 20th Century. His plan is to see that Bruce Banner's grandfather dies in the trenches during World War I. Then Banner wouldn't be born; the Hulk would never exist; and the Avengers would never form. Then there would be no one to stop Kang when he invaded (invades?) the 20th Century in Avengers #8.
He tries to do the job himself, but he's stopped by a "Time Storm" blanketing that era, forcing him to return to the 41st Century. (I have no idea what a Time Storm is, but then I'm not a 41st Century temporal physicist, so I have an excuse. What's yours?)
That means he has to find someone who can withstand the rigors of the Time Storm AND be willing to kill Bruce Banner. The obvious candidate is the Hulk--this was from a time when the big guy didn't realize he was also Banner and felt a strong hatred for his alter ego without knowing why.
So he teleports the Hulk aboard his ship, tells him how he can destroy Banner, then sends him back to World War I.
So far, the plot has been delightfully convoluted in a way that few fictional genres outside of comic books can get away with. But it gets even better. To make sure Banner's grandfather dies, the Hulk must stop the Phantom Eagle from destroying a giant cannon the Germans are using to shell Allied lines. If this happens,
The plan, though, goes awry when the Germans prove to be good shots with anti-aircraft guns. The Hulk takes a few hits while he's hurtling towards the Phantom Eagle's plan. Enraged by this, he switches direction in mid-air (I'm not sure how--he doesn't fly, he jumps) and destroys the German cannon himself. History then continues on more or less they way its supposed to.
It really is convoluted, especially for a single-issue story. But it works, because everything that happens follows a workable comic book logic and Herb Trimpe's art makes it all fun to look at. Heck, even the contrivance of a random Time Storm hanging over World War I is fine with me. That's the sort of thing that happens in a comic book universe.