Did automobiles replacing horses, diminishing horse population, diminishing horse suffering – as a consequence of work forced upon the animals. Is that moral win for horses; less suffering? Although their population is vastly smaller than 130 years ago.
The lack of individuals within a species is not a problem as long as the population is healthy. Horses are not in danger of going extinct. I do not know the numbers then and now, but horses are fine, and the ones alive in countries that would have put them to work in other eras are free of suffering, which is something every sentient being wants to avoid.
I’m glad horses are not being used as much as before; they are not objects, they are animals just like us.