To get the low-down on these "Ultra-Heroes" (The term used in the Mighty Comics of the 60s. Presumably a reaction to Marvel and DC trademarking "Super Hero.") you could do a lot worse than the MLJ Companion from TwoMorrows.
The history of the characters can be divided into publication eras. The Golden Age started with Pep Comics in 1940. The Shield would appear there, America's first flag-clad hero, 15 months before Captain America. The Comet was there, too, unusually violent, and ultimately the first superhero to die. The Hang Man and Black Hood followed, but all the superheroes ultimately gave way to Archie Andrews and the Riverdale gang.
With the dawn of the Silver Age, the MLJ superheroes were revived first in the Archie Adventure Series and then Mighty Comics. Joe Simon created the Fly, who was likely inspired by Captain Marvel (Shazam to kids today) and was perhaps one of the inspirations for Spider-Man. DC's success was the impetus for the revival, but Marvel's success guided its development. Jerry Seigel was brought in as main writer and either was trying to do a burlesque of the Marvel style or was unable to take it seriously. Either way, the Mighty Crusaders (as the new team was called) were "High Camp" a year before the Batman TV show made it the hip way to handle superheroes.
The campy 60s titles died away, but the heroes wouldn't stay down. They were brought back in the late 70s in reprints as part of the Red Circle line. The early 80s saw new stories produced, masterminded by Rich Buckler, with a grittier tone in keeping with the times and in some ways anticipating what was to come. Archie backed off from this pretty quickly, rebranding the line as the Archie Adventure Series again and making them more kid-friendly. They even got a toyline.
Archie Comics have been publishing the superheroes themselves since 2012, but it doesn't look like they've published anything since 2018. Given the Mighty Crusaders history, I suspect they'll be back. You can't keep the ultra-heroes down.