Your criticism is completely pointless.
I’m not sure what your expectation is, but even your claim about the assumption the paper makes is incorrect.
For one thing, the paper assumes that the amount that will be transferred from the human lawyer to the AI lawyer would be $500 + the productivity gains brought by AI, so more than 100%.
But that is irrelevant to the actual paper. You can apply whatever multiplier you want as long as the assumption that human labor will be replaced by AI labor holds true.
Because the actual nature of the future is irrelevant to the question the paper is answering.
The question the paper is answering is what impact such expectations of the future would have on today’s economy (limited to modeling the interest rate). Such a future need not arrive or even be possible as long as there is an expectation it may happen.
And future papers can model different variations on those expectations (so, for example, some may model that 20% of labor in the future will still be human, etc).
The important point as far as the paper is concerned is that the expectations of AI replacing human labor and some percentage of the wealth that was going to the human labor now accrues to the owner of the AI will lead to significant changes to current interest rates.
This is extremely useful and valuable information to model.