From a Game Design perspective: Backtracking is not a Core Mechanic of Survival Horror.
Per Definition "Survival" Core mechanics are: Scarcity of items (Ammo, Health etc)
Non-regenerating health
Enemies that are easy to beat as one but tough in a group.
Usually also underpowered Main characters that can only take a few hits.
Yes Resident Evil was important for Survival Horror even though you could argue Sweet Home on the NES invented it. But Resident Evil wasn't Survival Horror because you backtracked through a mansion. It was because you were underpowered, you had limited resources and item slots etc. You had to work with what you have to Survive
Backtracking can be one mechanic to support the core mechanics (you have to plan how to get back to a room) but again from a Game Design perspective it is not necessary since you can create the Dread of Survival Horror even without it. Dead Space did even in the Original and it was a Masterpiece of Survival Horror. It was about SURVIVING on a Space Ship overrun by otherworldly entities. Finding ways to dismember them and using your limited resources as a non action hero but simple Engineer.
So your Goalpost argument is a weak one because it is apples and Oranges. I mentioned the Key cards in Doom which is a much better comparison. Elements of early FPS was backtracking to rooms. It was part of the atmosphere, level design and a common theme be it Doom, Duke Nukem and even Quake. But it is not a Key Element to call it an FPS. And the same is true for Survival Horror.
Every Game in it's core is build on Pillars that determine every design choice you make. Backtracking is not one of the Core Design Pillars but part of Supporting Mechanics.
And this has nothing to do with being a "Survival Purist". These are principals that are taught in every Game Design course and most Game Designers know by heart.
First step is to decide on Emotions you want a player to feel. Then you decide on Core Pillars that achieve that (Scarcity, Vulnerability etc) and then you look how you can support them.
Basically you create Mechanics that through Dynamics (interaction with those mechanics) create Aesthetics (Emotions) in the player).
But we can open a separate topic for this. I did not know there are this many horror game fans are here.
