The thing is it doesn't need a huge leap in any specific thing, it needs a quantum leap in anything at all. Complexity only constrains you from solving all problems of a given type in reasonable time, not from solving any instance.
There are even many things that we already suspect are just engineering challenges. Like rocketry, hacking and robotics. Even if an AI can just act like a million engineers and scientists working for a decade per second, without any higher level of thinking, it could do some incredible things.
There are even many things that we already suspect are just engineering challenges. Like rocketry, hacking and robotics. Even if an AI can just act like a million engineers and scientists working for a decade per second, without any higher level of thinking, it could do some incredible things.