I'm surprised Biographics wasn't brought up in the OP. He falls under Quality Control, but as far as I know, it's just a small team that works on the videos (him included), though I'm not as sure on the possibility of studio backing. However, Simon Whistler (the host) appears to be a human content farm as he's admitted to having so many channels that he often forgets which one is for what. There's only one issue I've had thus far, and well, they say "show don't tell," so:
He should have just stated "I don't want Youtube to drop the ban-hammer on this channel, so..." Still, he just get points for saying "biologically male" instead of "assigned male at birth."
Moving on, Forgotten Lives covers obscure historical figures, but they do occasionally cover more well-known ones such as Calamity Jane. Legends of the Old West Podcast covers Old West history (Apache Wars, Billy The Kid, Red Cloud's War, etc.). It's run by Black Barrel Media and it's a godsend for anyone with even just a passing interest in Wild West history because it doesn't skimp over the mud and grit, never leaning one way or the other. Legacy of the Old West falls within the former's category. Infamous America Podcast (also run by BBM) covers true crime in America. Most Notorious, according to its channel description covers "Serial killers. Gangsters. Gunslingers. Victorian-era murderers. And that's just the tip of the iceberg." The host is author Erik Rivenes, and among the guests are: Paul Andrew Hutton (American culture historian), Charles Leerhsen (author of "Butch Cassidy: The True Story of an American Outlaw"), Vernon Keel (journalist and author), and many more. Based on a True Story Podcast covers the historical fact vs the historical fiction in movies, but also makes videos on how much of a movie could have happened (ex. How much of The Last Samurai could've actually happened?). Among its guests are: Dr. Brian Dirck (a Professor of History at Anderson University), Stephen L. Hardin (professor, historian and author), Joe Pistone (the real Donnie Brasco), and more.
Native American History is just starting out but what's quite noteworthy is that in their video on Comanches, they don't whitewash them. They paint them as the brutal mfers they were.