I don't disagree, but I think the evolution argument is a red herring. We didn't have to re-engineer horses from the ground up along evolutionary lines to get to much faster and more capable cars.
The evolution thing is kind of a red herring in that we probably don't have to artificially construct the process of evolution, though your reasoning isn't a good explanation for why the "evolution" reason is a red herring: Yeah, nature already established incomprehensibly complex organic systems in these life forms -- so we're benefiting from that. But the extent of our contribution is making some select animals mate with others. Hardly comparable to building our own replacement for some millennia of organic iteration/evolution. Luckily we probably don't actually need to do that to produce AGI.
Most arguments and discussions around AGI talk past each other about the definitions of what is wanted or expected, mostly because sentience, intelligence, consciousness are all unagreed upon definitions and therefore are undefined goals to build against.
Some people do expect AGI to be a faster horse; to be the next evolution of human intelligence that's similar to us in most respects but still "better" in some aspects. Others expect AGI to be the leap from horses to cars; the means to an end, a vehicle that takes us to new places faster, and in that case it doesn't need to resemble how we got to human intelligence at all.
True, but I think this reasoning is a category error: we were and are capable of rationally designing cars. We are not today doing the same thing with AI, we’re forced to optimize them instead. Yes, the structure that you optimize around is vitally important, but we’re still doing brute force rather than intelligent design at the end of the day. It’s not comparing like with like.