I think you don’t understand several aspects of Yudkowsky and Soares position.
Their position is not “LLMs scale directly to AGI” but “we are within 0-3 breakthroughs of transformers scale of AGI”, which is much less controversial.
Next, I think that everybody (LessWrong is not an exception) failed to do update on AI meta, following from existence of LLMs. Existence of LLMs says that there are brute-force-ish methods which create previously unimaginable gains in intelligence. It would be insane if transformer pretraining was the only such method which would also not reach general intelligence. Even if you are correct and there is a secret brain juice not present in current LLMs, it seems to be more likely that such hypothetical algorithm will coalesce in some sort of advanced, within 0-3 breakthroughs of scale of transformers, brute-force-ish neural net training process, than that it will be discovered by doing normal cognitive/AI/neuroscience. Humans are proven to suck in the latter and to excel in the former. Therefore, it seems to be the right strategy to put all compute under control.
Also you put too much weight on specific LLM properties as reasons for their current safety. Inside Y&S model, the main reason why LLMs are safe now is because they are not superintelligent, period. If you have something intelligent which can’t kill you, then you can hit it with wrench until it starts to output acceptable behavior. I think that if you presented modern AI safety community with black box running your hypothetical brain algorithm at speed and quality of 100IQ human and ability to receive whatever training data and reward schedule researchers choose, they would make it to output aligned behavior in six months, using methodology not dissimilar to modern LLM alignment methodology. The problem is that they would solve it using trial and error in a way that would kill everyone if they tried to do it with superintelligent black box.
You can dissassemble Earth really fast if you take enough fusion fuel (roughly in size of Starship) and use it to launch projectile at relativistic speed. You probably want to do it in somewhat more controllable fashion to not spill matter of Earth over all Solar System, but there is really nothing hard in making planet-busters if you have fusion.