I am wondering if the game advertised itself in anyway as inspired by the Metro series. I could see that causing potential issues but you are right. It does rapidly cascade if you take that approach.
The quote below is from an article with the author of the series and (TL:DR) they admit that they were inspired by the Fallout and Roadside Picnic.
I know Metro is a product of your environment, but I read earlier that you were inspired by the Fallout games…
Very much so by the first Fallout games. One of the sources of inspiration was Fallout 1 and 2, the isometric RPGs. And I was so inspired by Fallout when I was a student that once I went to cook my pasta and I was in such a hurry to get back to my desktop that I poured boiling spaghetti over my knees and luckily enough it was just inches away the most valuable thing that I have. That’s just to explain the extent of my passion for Fallout 2 back at the time. Also, not just that of course, but the books by the famous Soviet science fiction authors the Strugatsky brothers who wrote Roadside Picnic (Пикник на обочине), later adapted as Stalker and another work of theirs called The Doomed City (Град обреченный) which also has this incredible romanticism of abandoned urban spaces where you become the new master and you can explore the empty streets and empty buildings and everyone’s gone and you roam through empty apartments full of the belongings of other people. So this is something very romantic and very dreamy that can also be accounted for as an inspiration. And there’s some movies of course. There’s a very famous Soviet movie called The Letters of a Dead Man (Письма мёртвого человека), also about the post apocalypse. Altogether, that’s shaping your art references that inspire you. Then you build up on that and you become the inspiration for someone else and that’s how creative things work.
The Fallout games themselves were inspired by a multitude of works such as Mad Max, On the Beach, and A Boy and His Dog at the End of the World. There’s a PDF file out there that I believe was used during some kind of conference/convention talking in depth about this that I am struggling to find. It’s continued to do so throughout the series. I find this is most noticeable throughout Fallout New Vegas with many quest names and a chunk of dialogue referencing the material.
Kind of unrelated but interesting if you ever want to go down a rabbit hole you should check out how inspirational the book I Am Legend Is. It inspired The Omega Man and The Last Man on Earth and was incredibly significant in the creation of the zombie media going on to be the inspiration for Night of Living Dead.