I don't buy that basically because of what I already pointed out: that Twin Peaks purposely and consciously shows us that the dividing lines between worlds we inhabit (such as reality and dreams) are more tenuous than we think. The original series rotated on the device of Cooper and Laura Palmer having met each other at different points in their own timelines in the same dream, which is in fact a reality inside a different world. And again throughout this series, there are many references to the blurring of dreams and reality. The dreamer dreams and then lives inside the dream, but by living in the dream, something real is happening. Real life is happening in that dream. Dreamworlds in Twin Peaks are almost never just happening inside someone's head, so I think the interpretation that the whole thing was literally a dream that never existed in any way outside Cooper's mind is kind of a simple interpretation and I just feel it's very un-Lynch to do something like that. It seems much more likely it is intentionally impenetrable in its realness or fakeness.
Think about Audrey's story. She SEEMS to be asleep or in some kind of state of mental imprisonment, yet she is aware of characters living and breathing in the real Twin Peaks, and she even goes to the roadhouse although it is unclear whether she is really there, or if she is, if it's the same roadhouse we see in all the other roadhouse scenes. She says to Charlie that sometimes when things happen in dreams, they come true. The dreamer dreams and then lives inside the dream.