The fact that is a PR about the research (and consequently "dumbed down" for a lay audience) and not the actual research paper makes it a bit hard to divine, bu

The fact that is a PR about the research (and consequently "dumbed down" for a lay audience) and not the actual research paper makes it a bit hard to divine, but I'm pretty sure the authors didn't conflate grammar with inflection affixes. In fact, the section on "Defining complexity" in the article here does mention this: > "Many of the disagreements are down to differences in how 'complexity' is defined [...] In this study, we improved the methodology by teasing out two distinct measures: fusion (how many affixes verbs and nouns have) and informativity (how many distinctions are made)." It strikes me as more likely that they're focusing on easily quantifiable metrics of grammatical complexity. Without reading the paper myself, I'd guess that the metrics chosen here suffer from lamplight fallacy (they're focusing on what can be quantified because it can be quantified as opposed to working out what would be a useful guide).