Vocabulary is just as important as grammar
Without vocabulary, you will not have much to say even if you know how to say it. I'd say vocabulary is more important than grammar. I was raised in the USA until age 11, when I followed my divorced mother back to France, learned French, and went through the French school system.
The irony is that I left the US school system in Junior High School and right when we had started studying grammar, and I was integrated in the French school system the year after they had finished studying French grammar.
So I know how to speak, read and write in two languages better than many, but I don't have the faintest idea why. I can tell someone if what he wrote is correct or not, but I can never justify my opinion. It's always a "gut instinct".
The one thing that helped me was my voracious reading appetite. I love reading all kinds of things, and that brought me a vocabulary much greater than the SMS-toting kids have today. It also probably showed me all the grammar stuff that I missed in school, but absorbed through the millions of words I have read.
So, in fine, I would say that vocabulary is more important than grammar.
Now, concerning this article, I am rather disappointed about the science of it. We are told that the researcher determined that his simulations demonstrated the mathematical tendency of learning better with large words. Great ! Now how were those simulations programmed ? Do we now have a precise mathematical model of brain function ? I doubt that, so what was his computer model programmed with and how is that relevant to the subject studied ?
It's easy to program a computer to give the results one wants to have. What guarantees that that has not been done here ?
Pascal.