A crux here seems to be the question of how well the AGI can simulate physical systems. If it can simulate them perfectly, there’s no need for real-world R&D. If its simulations are below some (high) threshold fidelity, it’ll need actors in the physical world to conduct experiments for it, and that takes human time-scales.
A big point in favor of “sufficiently good simulation is possible” is that we know the relevant laws of physics for anything the AGI might need to take over the world. We do real-world experiments because we haven’t managed to write simulation software that implements these laws at sufficiently high fidelity and for sufficiently complex systems, and because the compute cost of doing so is enormous. But in 20 years, an AGI running on a giant compute farm might both write more efficient simulation codes and have enough compute to power them.
I believe 80000 hours has a lot more coaching capacity now, it might be worth asking again!