This is food for thought, but horses were a commodity; people are very much not interchangeable with each other. The BLS tracks ~1,000 different occupations. Each will fall to AI at a slightly different rate, and within each, there will be variations as well. But this doesn't mean it won't still subjectively happen "fast".

Whether people are interchangeable with each other isn't the point. The point is whether AI is interchangeable with jobs currently done by humans. Unless and until AI training requires 1000 different domain experts, the current projection is that at some point AI will be interchangeable with all kinds of humans...

That looks to me like there are ~1000 interchangeable economic human roles for AI to replace.

So I guess we should check to see if computers are good at scaling or doing things concurrently. If not, no worries!