Question: does the model account for general increase in energy use, within the timespan of (and, possibly, also as a consequence of) Bitcoin growing to reach that market cap, or is 0.74% just the absolute amount of energy as a cut of today's total usage?

If the latter, 0.74% seems less alarming, as it would surely be less when growth is accounted for, especially considering that some of this growth would likely (hypothetically) be driven by an increase in both production and consumption as a direct consequence of the use of Bitcoin, with all the benefits that brings.

But either way, it does still seem moderately alarming, albeit as a kneejerk reaction to the figure without much critical analysis. It's a very interesting economic question as to whether investing this order of energy consumption into Bitcoin would be worth it, both for individuals and for society(ies). I expect many an economics PhD will be minted on this very topic!