The real benefit of more #k's is not about the final image. It's about flexibility in post. A shot well exposed and composed will always look great, on any platform. The human eye can't tell the difference. But computers can. And it's when you have to push/pull the color/shadows, crop, stabilize, etc, that you'll miss those extra k's.
You nailed it when you said "effectively". One cannot gain more color information by downsampling 4k 4:2:0 8 bit to 1080p 4:4:4 10 bits. Downsampling interpolates (educated guess in layman's terms) the available information over the extra channels and bits, to allow us to work with it in post as 4:4:4 10 bits (more pixels and shades). This flexibility is all it buys you besides the sharper image.
Technically true 1080 10 bit 4:4:4 will always be more precise than a 2nd pass of interpolation. Although the human eye can't tell the difference anyways.
It was french students and it's barely similar. The only similarity is in the house floating away. Hardly qualifies as the same story. I'd say at most it was the inspiration. Here's the short in question.
How does a person know how much a movie is worth to them before they watch it? This experiment wasn't well thought out.
All the movies you mentioned were made for cheap IN COMPARISON to studio blockbusters. Even Reservoir Dogs was made for a cool million in the early 90's. Bottle Rocket? Same. And Kevin Smith has said that he doesn't think Clerks would get into Sundance nowadays. The expected quality of the films from unknown filmmakers is much higher now that Sundance gets around 5k submissions per year, compared to around 500 when Clerks got in. Unless you're a name, your cheap film isn't getting into Sundance. I find it hard to believe NO recent, cheap film from an unknown filmmaker has made a splash at Sundance. Is it really a lack of talent at that level?
Unfortunately even directors like Spielberg struggle to get their movies made at times. It took Spielberg years to get Lincoln off the ground, and it wasn't until Leonardo DiCaprio called and talked Daniel Day-Lewis into playing the lead that the studio greenlit it.