I'm not sure about the Boschian connection, but most of what's in Elden Ring isn't really "new". The vast majority of what's in Elden Ring is themes that From Software have been using for a long time, starting with Demon's Soul for some. I'm not sure about the origin of most though. Spoilers ahead, so don't read if you want to discover everything by yourself.

The most obvious one is as always the idea of stagnant water at the bottom that becomes corrupted, which from what I understand comes mostly from the asian religious ideas about impurity. I'm not sure if it's coming from Shinto or Buddhism, or something else, but there's always something about stagnant water/stagnation being "bad", and water at the bottom "washing away" impurities on the way and being the "worst". That's where the usual poison lake comes from. It's also a strong idea in Sekiro, with immortality coming from the heavens (with the divine dragon) and being corrupted on the way down (with the centipedes). Here in Elden Ring we have the lake of rot, the deeproot depths, and the bottom of the Haligtree.

Then there's the idea of a fallen empire hiding behind illusions. In DS1 Anor Londo was the prime example of that: everything is an illusion, that you can break. This was used here in Raya Lucaria: the Rennela that you fight is an illusion put here by Ranni, which mirrors Gwynvere/Gwyndolyn, and Fillianore. Rennela and Fillianore both hold an egg. I'm not sure about the reference here, there's the same theme in Angel's Egg by Mamoru Oshii, but maybe there are deeper origins.

There's the idea of some people living a corrupted form of life that still try to live their life "in peace": in Demon's Soul there's Maiden Astrea in the valley of defilement asking you to leave them alone, in DS1 there's the inhabitants of the painting (with Priscilla asking you to leave them alone), in DS3 the painting makes a comeback, with its inhabitants that want to rot in peace. In Sekiro, there's the monks in Senpo Temple, that acceeded to a corrupted form of immortality and are being devoured by insects/corrupted by centipede. There's the same in Elden Ring with Fia and those who live in death, and in a way the Haligtree people.

Lots of ideas are refinement of previous ideas: Rykkard seems to be a refinement of Aldrich as a "person in the world", and of the King of the Storm/Yohrm in terms of gameplay (Serpent Hunter is way more interesting than Storm Ruler). This one is a bit of a stretch, but Ranni's questline with Blaidd reminds me of the questline with the Painter and Gael. Both are about partially revolting against the order of this world to find a way outside the influence of the fire cycle/equivalent in Elden Ring. The smith at the hub is also an improvement: he gained a real personality, a real purpose. We meet again the last giant of his species that's already hurt when you meet him and removes one of his limb. Giants keep transforming into trees. Sorcerers doing too much research keep ending up in weird places (brain of mensis, the end of Sellen's questline). We went from giant crabs (there's a hilarious PC Gamer article about this) to giant crabs AND giant lobsters. There's something about Miquella (arm coming out of a coccoon, removed from a tree) and the curse-rotten greatwood, though I don't see much else about it. Maybe I'm missing some cultural references, maybe a DLC is coming, maybe it'll be refined in a next game/

All of that to say, it's nice to discover who Hieronymus Bosch is and what he did, but I wish the article instead focused on From Software themes and where they come from. Where do girl with eggs come from? Why are giants always corrupted in some way? What's the history of impurity in asian religions, and how did it influence From Software? We now have 7 games: Demon's Soul, Dark Souls, Dark Souls 2, Bloodborne, Dark Souls 3, Sekiro, Elden Ring. They slowly went from niche hits to a specific audience to a mainstream appeal. They come from a country with a rich culture, that's often seen through the lens of "weird Japan". They appeal to people through the gameplay, but also through the themes, the visuals, the gameplay. I think it's time to take them seriously as pieces of art by themselves.