You can tell this isn’t authentic, because they finished it.
I recently noticed that the Drowned God in the Game of Thrones series is quite similar to Cthulhu/Dagon.
There’s a similarity between its litany and the famous couplet from the Necronomicon:
What is dead may never die, but rises again, harder and stronger.
That is not dead which can eternal lie,
And with strange aeons even death may die.
The location of the cult, the Iron Islands, has the air of a sinister Lovecraftian small town such as Innsmouth, being poor, isolated, and hostile to outsiders (as well as, obviously, being by the sea).
The ruling family, the Greyjoys, also uses a kraken on its arms:
Obviously there’s no such thing as artwork being objectively right or wrong. But if the intention of an RPG cover is to interest the viewer and/or give them an idea what the product is about, then yes, they mostly fail.
I had a look at Amazon’s current listing of top-selling fantasy books today. There seem to be two main styles for the covers.
Obviously some RPGs are going to deliberately try for a comic book style. But this is the 4th edition Dungeon Master’s Guide 2:
It’s not a budget or skill issue either. I’m pretty confident that a ‘single symbol and text’ cover would be easier to do, or cheaper to commission, than full-page artwork of a PC vs monster skirmish. And there are lots of stock photos out there if you wanted to do the other main style.