> Or rather, a large organization could only avoid slowing down if they avoided tree structure. ... the only way I can imagine for larger groups to avoid tree structure would be to have no structure: to have each group actually be independent, and to work together the way components of a market economy do.

No need to imagine it — Ricardo Semler was already talking about and doing this in the 1990s. See https://en.wikipedia.org/wiki/Ricardo_Semler