So I think what most metamoderns/2R folks would agree on is that we need to move beyond both modernism and postmodernism. So in that sense they agree with a lot of the points you just made (so no need to start a new movement 
)
What there is disagreement on within the movement, I’d say, is whether postmodernism is a necessary step on the way to the next phase. The reason this is so hard to discuss is because postmodernism itself means so many things to different people (e.g. scepticism of grand narratives, cynicism, nihilism, relativism, identity politics…)
This is partly why I wrote The Rise of Scientific Grand Narratives - in which I tried to clarify at least one way in which postmodernism (in a very specific sense) could be a logical step towards metamodernism. But it’s a big area that I think could benefit from more research and discussion.