In actuality they are pure 2D games, and can be played purely from a 2D top-down perspective as there aren't any vertical aiming or other height elements.
While it's true that there is no vertical aiming/looking, Doom and Wolfenstein 3D simply would not be the same games if played from a top-down perspective.
The thing about the first-person perspective is that it's an entirely different angle from top-down. It's not prettier or uglier, nor better or worse; it's just different.
From a first-person point of view, you can see "infinitely" in one direction. Take the same scene and look at it from top-down. Your field of view changes drastically. You gain a peripheral advantage, but things far enough off in the distance will be cut entirely out of view. If you want to mimic first-person visibility from a top-down angle, you would have to zoom out until you can see the farthest corner of the room... But doing that would make the objects nearest to you tiny.
Yes, even in primitive games such as Wolfenstein 3D, first person perspective is justified.