Agreed or Disagree: Knowing a bizzilion words in a certain language, doesn't equal fluency in said language!

I recently got into a friend of mine who is a teacher (not a language teacher, but he is married to one) about language and fluency, and he kept insisting that knowing like 2000 words means you are at this level and knowing 5000 words means you are at this level and so on

He is a stubborn one but my argument was that, even IF someone knows a million words or whatever, it doesn't necessarily mean that they can understand them in conversations or use them properly in sentences or even speak them, there are alot better metrics for fluency than knowing an arbitrary number of words!

But what do you think?