I think you missed my point. I did say flight is preferable in most situations. But horses are still a useful addition to the game as they can be found and utilised long before you have the necessary resources to build a jetpack. And if you had to cross a section of land (with no large bodies of water) a horse would be the superior option as it is much faster. Mobs are not really a concern when you can just blitz by them.
As for minecarts, they serve a different purpose. Minecarts are mostly for getting from point A to point B, and transferring items across long distances using chest minecarts. A big disadvantage they have is that they require setup in the form of laying tracks. Horses do not require any setup process, and they can travel at approximately the same speed as a minecart on powered rails. If anything, it's minecarts that have now become less useful.