This is utter rubbish. Nobody learns to speak any language as an adult without an accent. That has nothing to do with phonological complexity, that's just how we're wired. Spanish may be easy to describe on a blackboard, but don't tell me that people who learn Spanish as a second language later on don't have accents. And languages don't succeed because of linguistics, they succeed because of politics. As someone whos…
As such the author may be unknowingly over-emphasizing the role of distinct vowel pronunciations, assigning their importance to intelligibility or understanding rather than merely to accent.