Nothing in the article contradicts that 'fact'. The question is only whether the development of eukaryotes involved other significant steps in addition to the m

Nothing in the article contradicts that 'fact'. The question is only whether the development of eukaryotes involved other significant steps in addition to the mitochondrial endosymbiotic event, or whether the latter event was all that really mattered. In both cases, subsequent development of eukaryotes and hence multicellularity depended on the seemingly very rare endosymbiotic event.