However, it is much more of an open question in computer science if we will ever be able to greatly improve on the statistical inference algorithm used in the cortex. It is quite possible that evolution had enough time to solve that problem completely - or at least reach some nearly global maxima.

This is unlikely. We haven't been selected based on sheer brain power or brain inefficiency. Humans have been selected by their ability to reproduce in a complicated environment. Efficient intelligence helps, but there's selection for a lot of other things, such as good immune systems and decent muscle systems. A lot of the selection that was brain selection was probably simply around the fantastically complicated set of tasks involved in navigating human societies. Note that human brain size on average has decreased over the last 50,000 years. Humans are subject to a lot of different selection pressures.

(Tangent: This is related to how at a very vague level we should expect genetic algorithms to outperform evolution at optimizing tasks. Genetic algorithms can select for narrow task completion goals, rather than select in a constantly changing environment with competition and interaction between the various entities being bred.)