All the big named signatories to this were transparently self interested, as well as not real "practitioners" - mostly adjacent folks upset to be out of the limelight. I know it's a blurry line, but people like Andrew Ng and Yann LeCunn who are actually building ML stuff have dismissed this outright. It's almost like a bunch of sore losers got together and took an irrelevant stand. Like Neil Young and Joni Mitchell vs Spotify.
I mean then what is the basis for calling him not a "real practitioner" while Yann LeCun is? It seems a little unfair to dismiss outright the opinion on a deep learning technology from a guy who won a Turing award for research into deep learning. I also don't see any evidence that he is "transparently self-interested."