Yes, you’ve paraphrased the argument well.
While progress for any certain technology can certainly be exponential, the benefit or impact of it may not be exponential if we assume that the lowest hanging fruits (in terms of cost/benefit tradeoff) gets plucked first, and then it becomes harder and harder to derive economically relevant benefit even with tech progress.
What unbounded benefit relies on whether we can keep on discovering new types of general-purpose technologies, and not just an improvement in current technologies.
E.g. faster air travel depends on some new uncertain technology to be invented. We can only squeeze incremental benefits from further improving the current air travel technologies.
Also see Eroom’s law which suggests declining R&D productivity for drug discovery.
Whether we can keep on discovering such general-purpose technologies is pure speculation, so there’s some probability that we may actually not be in a weird cross-roads within the next 200 years.
This is interesting. I agree that the various cleanup technologies add to the economic growth.
My point was more suggestive in the sense of whether that poses a practical constraint to economic growth (in terms of say negative feedback loops) when the cost of cleanup outstrips the benefit derived (and hence putting an upper limit to the desire of the benefit).