> This argument requires us to believe that AI will just asymptote and not get materially better.

That's not what asymptote means. Presumably what you mean is the curve levelling off, which it already is.

This seems overly pedantic. The intended meaning is clear.

Hardly, asymptotic behavior can be anything, in fact that's the whole question: what happens to AI performance as we tend to infinity? Asymptoting to `y = x` is very different to levelling off.