People have an advantage that horses don't have: people can own property, and they have legal rights, like the ability to vote in elections. When we're talking about AI, though, it's not too hard to imagine computer programs eventually being allowed to legally own things and accrue wealth. It's harder to imagine them being allowed to vote (how would that even work?) but something like it could happen. We can also imagine this going the other way: economically "useless" people losing the right to own property or the right to vote. Or if the rights continue to exist in theory, in practice they become poor and disenfranchised. And then "the strong do what they will and the weak suffer what they must." It happens all the time.

I think in the long run we need to figure out a reasonable economic system that can deal with abundance of the things people want/need, and scarcity of work. Maybe it's as simple as making a 30, or a 20 hour work week the norm. The default alternative seems to be to have more and more people fighting for fewer and fewer jobs, to the point where everyone who has a job has to work extremely hard under long hours and bad conditions for low pay because if they don't there's ten more people ready to take their place at the drop of a hat.