Speed is king in the open world. Some mounts should allow mounted combat and others shouldn't to be able to help balance the game. (Or have severe penalties)
I'm going to give a random example here to illustrate what I mean.
Let's say only Jotun horses (random horse don't focus on this) are the only horses you can do mounted combat from and not be gimped. You can now balance Jotun horses around combat effectiveness, you can increase their health and natural armor, you can further specialize the animal and balance it accordingly.
Right now since all mounted combat can be done on all the available mounts effectively and gankers have a huge advantage. In the open world mobility is key.
You could even add a massive mounted combat penalty to certain mounts if not outright preventing it, like massive stamina drain / damage reduction / move speed reduction.
If you allow mounted combat to operate just as efficiently on every type of mount the fastest mounts will be used by gankers and small group and solo players will just leave the game. Ganking is the lowest form of PvP, it's fun to shit stomp noobs but it shouldn't be as easy as it is. You should be able to somewhat reliably escape ganks. The gankers should have to put in work.
The major benefit of doing something like this is all the sudden you can start balancing specific mounts more to fill a niche. Sure desert horses are the fastest but maybe you can't fight from them effectively or at all and they're harder to take down. Maybe steppe horses get more HP but can't wear bags and the excel for mounted melee.
Otherwise it's just going to be the same as the crafting system where sure there may technically be millions of choices but realistically people use like 4 different resources
I'm going to give a random example here to illustrate what I mean.
Let's say only Jotun horses (random horse don't focus on this) are the only horses you can do mounted combat from and not be gimped. You can now balance Jotun horses around combat effectiveness, you can increase their health and natural armor, you can further specialize the animal and balance it accordingly.
Right now since all mounted combat can be done on all the available mounts effectively and gankers have a huge advantage. In the open world mobility is key.
You could even add a massive mounted combat penalty to certain mounts if not outright preventing it, like massive stamina drain / damage reduction / move speed reduction.
If you allow mounted combat to operate just as efficiently on every type of mount the fastest mounts will be used by gankers and small group and solo players will just leave the game. Ganking is the lowest form of PvP, it's fun to shit stomp noobs but it shouldn't be as easy as it is. You should be able to somewhat reliably escape ganks. The gankers should have to put in work.
The major benefit of doing something like this is all the sudden you can start balancing specific mounts more to fill a niche. Sure desert horses are the fastest but maybe you can't fight from them effectively or at all and they're harder to take down. Maybe steppe horses get more HP but can't wear bags and the excel for mounted melee.
Otherwise it's just going to be the same as the crafting system where sure there may technically be millions of choices but realistically people use like 4 different resources