Funny thing, when I was working at Iron Lore on the Black Legion concept, a new designer we hired, asked if I’d ever read Glen Cook’s Black Company, which I hadn’t and suggested I check it out, since he said there were a lot of parallels (not least the name) with the backstory I was working on. So I ended up reading through the Black Company series and then sometime after, I found out about Steven Erikson, which is sort of a ripoff of Black Company and did read a bunch of his books, which in some ways are better written than Cook’s… but they’re so long and convoluted I kind of got burnt out at some point. I forget where I stopped.
Really though, I think a lot of similar in fantasy is due to the fact that we’re all ripping off the originals - history / ancient mythology and the reason for that is that it was forged out of the human experience and contains age-old motifs that resonate with us and are broadly relatable. That and they just were there first to lay claim to a lot of the cliché cool ideas we continue to recycle. I majored in ancient history and, like I me, I can tell Erikson really digs ancient history and myth and was heavily influenced by it. Notably the feel of it, where stuff is often a lot more gritty and messy than tolkien style fantasy, what with all the child eating, patricide, eagles feasting on livers and such.
A lot of the stuff in the original comparison came before I read Malazan, so it’s definitely not influenced by it. Other stuff, I honestly couldn’t say, sometimes you don’t directly borrow an idea but maybe you were subconsciously influenced by it? Other stuff mentioned above, Zantai came up with and he didn’t Steven Erikson or Glen Cook.
I don’t really remember where a lot of ideas came from if anywhere, but Ch’thon and all the undesirable early creations cast into the void is a total ripoff of Cronus and the titans of Greek myth, which is probably what inspired Erikson. I’ve actually not read the myth of Kingu somehow, so also a coincidence. I just was trying to come up with my own creation myth and there is more creation backstory that isn’t conveyed in GD (I feel like to create depth, sometimes you need to have supporting story and events that you never explicitly reveal but which provide coherent foundation for the story you do tell). Basically though, the origin of the gods has to do with the joining of matter, energy and spirit, and so to create life and sentience, those elements had to come from somewhere. Part of the fucked up truth of Cairn is the humanity was created from the sacrificing of Ch’thon and so part of his madness lives in all people.
Chaos - I mean, that’s in like every mythos and fantasy world. I think we only really added chaos because we needed another damage type, which originally was only meant for enemies. Not like it was a very original idea.
Mogdrogen - I think I finally got around to watching Princess Mononoke at the end of Iron Lore, because someone had a poster or something of it in their cubical and I thought “a giant wolf god would be cool”. Then came up with the titan backstory and eventually decided it should be able to change into a human form because it would be weird every trying to allow the player to talk to a screen-sized wolf.
Menhir - I kind of feel like I shouldn’t reveal some of this stuff because I’m showing too much of how the sausage is made, so to speak and maybe taking some magic out of it. However, Menhir came about because I was working on soldier and decided some skills should refer to dieties or people to add flavor and a feeling of depth. So I thought - defensive skills could be related to some earth god cuz like mountains are tough lol… So I vaguely remembered there was some word for ancient stone monoliths that was cool and looked it up - bam, Menhir. At that point, there was no backstory, existed purely to provide a cool context for skills. Honestly, a lot of GD lore came about like this - it started kind of shallow, as just some name / vague concept, then later we ended up filling a lot of it in with lore as the need arose. The cleaving mountains with mythical weapons thing was from Zantai - this is actually my first time reading it… sounds a little far fetched for my taste 
Oleron was actually a story I came up with working on the Black Legion concept, so it predates my having read Erikson. I then decided to recycle it for soldier mastery because I like the name / figured the story fit pretty well.
Autumn Boar - we needed a few more constellation and I don’t remember who came up with them but I think we just tossed a bunch of different animals out there and Zantai wrote up the backstories.
It’s funny because there’s a number of deities in the constellations that exist purely to provide constellations to put points into - but some of them we’re now taking to expanding on for lore / backstory in the RTS.
John Bourbon - I honestly have no idea here… I think I was just trying to come up with a name that sounded cool and grizzled?
Aetherials are basically pissed off angels. Hey, not that I say it like that, maybe it was influenced by Supernatural? I have no idea at this point.
You missed probably the biggest influence though - Demolitionists. They aren’t called that in the books and I forget the details now, its been so long but I remember they had soldiers who were basically explosives experts. This goes back to Glen Cook though and Erikson borrowed from him.
Ultimately, virtually nothing emerges from the void as a totally original idea and, consuming so much sci-fi and fantasy content, it’s hard to even know sometimes where ideas may have come from sometimes. When I try to think up important char names, I look them up on the internet to make sure I’m not accidentally subconsciously stealing some name I heard somewhere else. A lot of people also tend to have convergent ideas, just based on the influences of the time - I mean, look how often I somehow happen to embark upon a project in a previously under-served genre and bam, suddenly everyone and their mom has had the same idea and is announcing new games in that genre…