To put it into perspective if you can run the human architecture on an AGI at a billion operations per second it's like compressing a historical human civilization of learning into a couple hours.
Maybe for some reason this learning process will be slow or maybe there's some reason why it can't scale up quickly, but based on the learning speed in narrow areas that seems unlikely.
There's also the fact that natural selection which is a relatively brute force sexual selection mechanism still results in general problem solving brains being everywhere - it doesn't seem like something particularly rare.
Maybe a single human, but can you run an entire world civilization and it's environment (basically Earth) in a sped up manner? Because one super fast human-level intelligence is still constrained in a way that all of civilization is not. What is one human sped up a billion times? Is that 1 billion humans? We already have several of those units operating around the clock. And those units have access to the world's resources, whereas one sped-up mind will not, unless it can gain control of the world.
You may not need that much access to the world to learn/infer a lot about it [1] and if a superintelligent AI needed access to more in order to achieve its goal it'd probably be able to get it.
[1] https://www.lesswrong.com/posts/5wMcKNAwB6X4mp9og/that-alien...
Once there's a way to train a general intelligence it's likely hard to contain the improvement - that's why the goal alignment problem is important. Even the current human architecture running at a billion operations per second instead of its current 100 or so would be a problem.
Human general intelligence is constrained by things like power consumption available via eating or needing a head that can fit out of a birth canal - AGI constraints are a lot less limiting and AGI can improve faster.