yes!!!!!!!! horses can carry 20% of their own weight, with the build (slender, lightweight horses can carry less than let's say,  heavy built, huge horses) they have plays a major role in it!!! donkeys and other types of equines (except zebras, which cannot be ridden at all,) can carry 20-30%, and ponies can also carry 20% of their body weight, but for all of these animals, it's advised to have less weight on them for as less time as possible in order to not tire them out. additionally, their equip load (which includes their rider and their belongings, such as bags attached to their sides) should be evenly contributed on both sides for less strain. it's really all about the actual breed + size of the horse, though, since they need to be strong enough to actually last for a long time when transporting people or items.

for actual numbers, it's stated that a 1000 pound horse can carry a 200 pound person. for normal people measurements, that's a~450 kg (small) horse with a 90 kg person on top of it. the heavier breeds of horses could probably also take in fat people & heavy cargo pretty comfortably.

the best part of any mmorpg was the introduction of all those crazy mounts like the dragons and the gigantic big cats!! they really should've added things like unicorn or pegasi or something of a cool horse with them though, like, give the original mount animals some respect!