You see there is very noticeable differene in speed between deserts and steppes. I don't have the precise numbers but if you're using unencumbered desert horse, you will always catch up to anyone else with any other kind of horse no matter what. So ofc when you're in a larger group and you decide to RPK, using good horses comes at almost no danger while the benefits are huge.
As long as you murder groups smaller then you or just solo players, chances of losing a single horse and almost 0 while the chance of always catching up and killing your prey is basically guaranteed. And even if by any chance you meet a bigger group, you're all on best horses in the game so you can get away pretty well.
So yeah, animal tamers go all the way to meduli and bring largre groups of these horses back, level them up fast and sell them for a pretty coin. And ofc these horses very likely will sell since they're worth it if you have a good utilisation for them.