I'm can't say I'm familiar with what StarWarsTheory says about the lore. But basically my view is the more involved George Lucas was in the production of content, or the more in-line that content is with Lucas' canon and his plans for the series, then the more "canon" that content is.
I agree that good things have been made since the Disney acquisition like Rogue One, Andor, Tales of the Jedi, the Order 66 arc of The Clone Wars Season 7, and the first two seasons of The Mandalorian. Not only are they well-made, but they fit in well with the canon. Whereas stuff like the Sequel trilogy, Rebels, Obi-Wan Kenobi, and Ahsoka are not only poorly made but also don't fit as well with Lucas' vision for the series. And the content made by Lucas' apparent successor Dave Filoni has had mixed success overall.
As for Legends, I agree it can get pretty nonsensical. There is an insane amount of content out there, but a lot of it is more "canon" than the recent stuff in my view. Things like the Thrawn books, the Force Unleashed video games, and Gennady Tartakovsky's Clone Wars series. Heck, I consider Robot Chicken skits like The Emperor's phone call to be more "canon" than the entire sequel trilogy.
If only Lucas never sold the franchise. We could have seen his sequel trilogy, not to mention those unfinished Clone Wars episodes instead of it being cancelled for Rebels. But maybe we didn't deserve it after all the hate his prequel trilogy got. The world just wasn't ready for it.