I would maybe agree with you if the entire realm of human existence was limited to words. There are many human experiences that transcend text, and indeed can hardly be adequately described using text.
Sure, it's the best we have online, but that does not make "the internet" the sum of all human experience. To reduce all of humanity down to the text on the internet is reducing us to the level of machines to fit the requirement of what a machine can process / simulate.
I don't think they're asserting that all of human existence can be subsumed as text, though? Just that "consciousness", or "understanding", in some meaningful sense could be exhibited by a system that can only interact with the world through text?
In the life of humanity, text has only existed a relatively short time.