Hmm. Oh idk. I never beat Journey but if it's like Flower it's not a walking sim, Flower definitely had gameplay and traditional levels and aspects of a video game but just set up oddly for ease of gameplay and it is a 10/10. Then again Abzu definetly feels very walking sim but instead of walking it's swimming, didn't finish past the first hour so can't judge. As for SOMA it's in that weird space where it's a walking sim mixed with Adventure elements but definetly a walking sim as with Nobody wants to die which is a more conplex walking sim, they have interactive elements but so does Still Wakes the Deep with pulling levers and Gone Home with it's puzzle but it's all very surface level.
I also think there is a ceiling to walking sims, perhaps they can be a 10/10 but they need way more effort and that effort has yet to come. They should be ahead of normal games by a long shot with graphics, VA, story etc and feel lime a geberation leap and have a story that beats the best of any medium. SOMA lacked the VA and a few other details but definetly could have been a 10/10 with a few tweaks and if it had interactibility and actual choices not like the facade of Nobody wants to die or two ending based on one decision but actual choice like Robocop Rougue city another game which is has walking aim elements. Death Stranding does not count but I can see why people would think it, there are way too many features, gamepkay elements and traditional camera snatching cutscenes. I wanna see the genre evolve into something like Robocop mixed with Detroit Become Human but keep the same general features.

Flower and Journey are listed as 'art game' for genre. Yet Journey is included in walking sim lists all over the place.

"Art games" and "walking simulators" are not mutually exclusive and can often overlap, particularly when focusing on artistic expression and narrative exploration. While "walking simulators" are a specific subgenre emphasizing story and atmosphere, "art games" are a broader term encompassing any game designed to emphasize art and/or evoke a specific emotional or intellectual response.

To make matters more confusing Dear Esther is officially listed as "Art Game", The Stanley Parable as "Interactive fiction", Firewatch is actually listed as "Walking simulator"

The definition of walking simulator is

"A genre of adventure games where the primary focus is on movement and exploration"

Death Stranding doesn't cut it, combat rules it out. Journey and Firewatch do fit.

Dear Esther is often said to be the pioneer of walking simulators, yet they go all the way back to The Forest on ZX Spectrum. Dear Esther was first release in 2008 as a source mod for HL2 called Esther at the time. Yume Nikki came before that in 2004.

Esther was great at its time, but imo surpassed by The vanishing of Ethan Carter.

One hidden gem on PSVR is Here They Lie, hampered by low resolution but oddly weird and fantastic.

It must have done something right for it to still be vivid in my memories.

Walking simulators are perfect for VR.

Maybe Journey and Firewatch 'officially' fit the bill, but they definitely don't fit my understanding of a walking simulator. Of course evidently I'm no expert on walking simulators. On the other hand, say, half of Death Stranding fits the description just as well (but the other half doesn't). My point? I don't think I really have one, I don't really care much to argue about what is usually considered a walking simulator and what isn't, since there already seems to be a pretty widely agreed consensus. Still, the borders of the genre don't really seem to be clear to everyone, as is also evident in this thread. I would guess it's because it's not a genre all that many people are very familiar with.

Saying a walking sim can’t be a 10/10 is like saying a movie can’t be a 10/10. It doesn’t have the interactivity of other video games, but that’s not what they are trying to be, they are different experiences.
Journey, The Stanley Parable and What Remains of Edith Finch are all in the 9/10-10/10 territory for me. Despite it’s praise, Gone Home did not impress me all that much, but it was still okay.