Much of these threads make the binary mistake: can these systems be compared, or are they fundamentally different? A bit of both, almost certainly.

This echoes an extremely naive view of evolution.

There are many phenotypes in the living world which have evolved but for which there is no reason to believe that the phenotype is either (a) supremely efficient and/or (b) under selection pressure (the two are obviously related).

Evolution has no tautology. Brains do not evolve to be supremely efficient, just like humans do not evolve to be supremely efficient.

What exists today is that which has survived, for whatever reason. It's not even possible to say something as apparently simplistic as "the only purpose evolution respects is leaving behind more copies" because that ignores (a) group selection (b) changing ecosystems that favor plasticity in the long run.

Not really, evolution doesn't guarantee the brain will be supremely efficient. It just guarantees that it will be efficient ENOUGH.

https://en.m.wikipedia.org/wiki/Catastrophic_interference

Which practically requires full retraining at every step to integrate new knowledge. I think we have some partial solutions like learning to select between finetunings, but not if the task needs to crosscut between them.

The human brain doesn't seem to suffer with catastrophic interference to nearly the same degree, independent of its computational efficiency, though there are possibly related things like developmental stages that if they are delayed may never be able to take place.