First off, apologies to my anon friend in advance for riffing off of his skewed thinking. He's not wrong necessarily, because he was probably addressing a specific client-case, but then again, he did not make that obvious in his tweet, so I feel the need to correct it.
The key is to deliver clear value in an acceptable format. It is possible to create a 'newsletter' in a solid format with content that no-one cares about. But, its also very likely that lots of people would signup for "One solid piece of actionable advice that can change the trajectory of your business, delivered once a week." It is also true that people respond to incentives. Even otherwise lame newsletters can reach an audience if they trade something of value for the privilege to spam your inbox.
Its easy to start feeling this way about email newsletters because we see lots of clients doing it wrong and offering things that people don't generally care about, and then not lifting a finger to promote it. But, even in these snowballs-chance-that-someone-cares situations (oftentimes our perception), keep in mind that there is an audience for just about everything, and early success is tied more to tactics employed to capture some of that existing audience than it is about creating the most whiz-bang content ever. You have to start somewhere, and the content can improve over time as you learn what people react tp.
I, for one, am glad that the expressed perspective exists. Because it means that less and less people are likely to take email seriously as a platform. This means there's more time for you and I to actually capture an audience.