And hardware overhang (faster computers developed before general cognitive algorithms, first AGI taking over all the supercomputers on the Internet) and fast infrastructure (molecular nanotechnology) and many other inconvenient ideas.

Also if you strip away the talk about "imbalance" what it works out to is that there's a self-contained functioning creature, the chimpanzee, and natural selection burps into it a percentage more complexity and quadruple the computing power, and it makes a huge jump in capability. Nothing is offered to support the assertion that this is the only such jump which exists, except the bare assertion itself. Chimpanzees were not "lopsided", they were complete packages designed for an environment; it turned out there were things that could be done which created a huge increase in optimization power (calling this "symbolic processing" assumes a particular theory of mind, and I think it is mistaken) and perhaps there are yet more things like that, such as, oh, say, self-modification of code.