You currently have the pace of total progress growing exponentially as AI improves. And this leads the bad back-predictions that the pace of progress used to be much slower.
I think your back predictions would be fine if you said that total progress = human-driven progress + AI-driven progress, and then had only the AI part grow exponentially.
Then in the back prediction the AI part would rapidly shrink but the human part would remain.
Re intermediate speed ups : a simple fix
You currently have the pace of total progress growing exponentially as AI improves. And this leads the bad back-predictions that the pace of progress used to be much slower.
I think your back predictions would be fine if you said that total progress = human-driven progress + AI-driven progress, and then had only the AI part grow exponentially.
Then in the back prediction the AI part would rapidly shrink but the human part would remain.