Well, what I can't stop seeing, is this:



(full disclosure: didn't get any immediate hits from a web search, so I used DALL-E to generate the image)

But seriously, the dot pattern from the holes in the basket look pretty similar shade and evenly cover the full pattern, so I think that implies a pretty uniform extraction. The Rorschach-y blotch near the center is probably just from the last drops of espresso outside the basket getting sucked back up into the puck when the 3-way valve is opened - or perhaps it's a ghost image of the critter that was climbing around the coffee plant you're drinking from

You might be able to test the paper's ability to show channeling, by deliberately creating one to see what it looks like: use a toothpick to poke a hole from top to bottom of the tamped puck before pulling the shot. I wouldn't suggest doing that with a roast that deverses better treatment, but one way to find the edge of a cliff is by driving off of it.

Just a theory: the paper inserts a thin, non-soluble membrane in the path of the fluid, kinda like a basket with a gazillion holes, which creates a short, lateral flow as the fluid directs into the actual basket holes. That lateral flow may create a more uniform distribution of flow and pressure, leading to multiple streams. The bottom of my VST basket is slightly bowed, so eventually my streams coalesce, roughly at the 1:1 brew ratio mark.

Keep in mind that the Chemex paper has thicker and thinner areas, it's not perfectly uniform. See 2:00 in this video for a microscopic examination of Chemex filter paper dry and wet.