This is true. The Preacher says,
“Do not be rash with your mouth, And let not your heart utter anything hastily before God. For God is in heaven, and you on earth; Therefore let your words be few. For a dream comes through much activity, And a fool’s voice is known by his many words.” -Ecclesiastes 5:2
"Answer not a fool according to his folly, lest you be like him yourself. Answer a fool according to his folly (some translations "as his folly deserves"), lest he be wise in his own eyes." - Proverbs 26:4,5
I think part of what's happening is that the bad ideas and bad reasoning get diluted among 9000 words and 100 references. It's hard to put your finger on one sentence and say "here's where you're wrong", because the conclusion does not (obviously) rest on any one sentence. It rests more on the volume of words.
But "proof by volume" is not actually a thing. (I mean, it's a technique that can be effective in practice, but logically, it's not valid whatsoever.)
How do you answer something like that? If you try a point-by-point rebuttal, you're going to be into it 9000 words yourself (at least), and it is rarely worth it. I think that's "don't answer a fool according to his folly".
"Answer him as his folly deserves" is less clear to me. Is that to just flat out say that his ideas are foolish? Is it to give a concise one-paragraph statement of why his conclusion is folly? I think the latter is preferable (if you can). I mean, the rationalist is just going to claim that you haven't engaged with his arguments, though you can reply "no I didn't; your conclusion is so wrong that I don't need to engage with how you got there". And the concise rebuttal may be helpful to bystanders.