The Blinded condition says that the creature "can't see". That seems pretty total to me. I think reinterpreting the condition to be "able to see, but not well" is a great way to fix the problematic interactions with Heavy Obscurement, but that approach both goes against the text and may produce other problems when you want the Blinded condition to actually mean "can't see", like with the Blindness/Deafness spell.
If it was a dark wall seen against a dark background, I would agree--the character wouldn't be able to visually discern the presence of the wall. But there's a lit background here seen through the door, so in the real world the wall would be seen by the fact that it interrupts that lit background (i.e. the wall is silhouetted against a lit background).
To clarify the purpose of the transparent-wall example, I'm not saying that the Darkness spell needs to be an opaque ink-blot because otherwise creatures can see through walls. I'm saying that the rules for darkness/vision/obscurement are not comprehensive, and contain contradictions that require every DM to make decisions about how they want to run darkness/vision/obscurement. In particular, I'm saying there is a contradiction in the rules between being unable to see an obstruction and that obstruction remaining opaque if the obstruction is backlit. Running the Darkness as akin to normal darkness happens to run into this already-existing contradiction in the rules.
I see this contradiction as pretty straightforward (but apparently am terrible at explaining it!): if there's a big opaque object/creature standing in darkness between an observer and a well-lit background, then in the real world the observer can see the big opaque object/creature because it obstructs the well-lit background (i.e. it's silhouetted). D&D doesn't have rules for silhouettes, so the DM has to decide whether to include silhouettes in their game or not. If they do let observers see heavily obscured objects/creatures as silhouettes, the DM isn't giving full effect to the Blinded condition--the observer is able to see something the Blinded condition says they can't. By contrast, if the DM does not let observers see heavily obscured objects/creatures as silhouettes, then, by definition, the object/creature isn't obstructing the well-lit background, and so must not be opaque.
Obviously, I expect every DM to work around this contradiction in one way or another--that's the DM's job. Multiple ways to adapt/reinterpret the rules have been presented in this thread that would work well.
I saw it and replied directly quite awhile ago. "Blind" in the real world may not mean "can't see", but in D&D that's exactly what the Blinded condition says. That means that not everyone who would be considered legally blind in the real world would have the Blinded condition in D&D. By contrast, everyone trying to look into a heavily obscured area in D&D does (effectively) have the Blinded condition.
I read "effectively has the Blinded condition" as "takes penalties as if they had the Blinded condition". I don't think "effectively" can be used as a synonym for "partially", particularly since D&D conditions are binary in every other context with which I am familiar. One could decide instead to ad-hoc the penalties inflicted by each condition based on the circumstances, but that would seem to negate the entire point of having codified conditions in the first place.