He never made claim that English is kinda a pro-drop language. His argument that it's easy to make a binary statement that Spanish is a pro-drop language and English is not, but reality is messy. He shows counter example in English, might not be common, nothing is stopping English from evolving like that. No matter the rules, trying to describe natural languages with rules always breaks down, the exception just grows. I think his argument was well presented, we can't brush off probabilistic models because we don't understand it all when they work so well. This essay is 15 years old way before the LLMs of today. It would be interesting to see his additional take on it.