If quantum biology is a thing, reality “computes” more efficiently than any computer.
Doesn't Arthur Clarke's quote, "Any sufficiently advanced technology is indistinguishable from magic," that I believe you used in another post, imply that the type of "computer" needed to simulate the universe is completely possible?
It makes sense that the universe would be the most efficient system for "calculating" itself as nature tends not to be wasteful. I would only mention the existence of analog computing. It doesn't change the conclusion of your analysis-- analog computing can provide, at best, several orders of magnitude of increased computational performance, not enough to grow exponentially with the number of particles being simulated, but enough to suggest that digital-quantum hybrid computing will (or maybe already is) occupying a niche analogous to digital-analog hybrids in the 1950's and 60's. Perhaps digital-quantum hybrid computers could more easily solve some of the multi-particle quantum interactions hinted at by the DNA and photosynthesis processes you've mentioned.