I am so glad someone else called this out, I was reading the napkin math portions and struggling to see how the numbers really worked out and I think you hit the nail on the head. The author is assuming 'essentially free' input token cost and extrapolating in a business model that doesn't seem to connect directly to any claimed 'usefulness'. I think the bias on this is stated in the beginning of the article clearly as the author assumes 'given how useful the current models are...'. That is not a very scientific starting point and I think it leads to reasoning errors within the business model he posits here.

There were some oddities with the numbers themselves as well but I think it was all within rounding, though it would have been nice for the author to spell it out when he rounded some important numbers (~s don't tell me a whole lot).

TL;DR I totally agree, there are some napkin math issues going on here that make this pretty hard to see as a very useful stress test of cost.