Too generalised for me because there are different types of hair in both horse and boar but they tend to even out as they are broken in.I view horse as the poor man's boar, they never quite feel as good, and after a time they get moppy and start shedding. Many modern horse brushes are too soft and flimsy, too much mane and not enough tail hair, they're made for modern "men". If you can find a vintage Ever~Ready brown horse hair brush get it, they beat all the modern ones by a mile.
Looking at my boar brushes, my Semogue 810 and 820 were much softer than my relatively cheap Omega 10065 but after breaking in the only difference is that the Semogue is bushier but the shaving performace of both is much the same.
With horse there is less variation between the two main types, mane and tail. But there is the rather confusing "50/50" which is mainly undefined: We take it to mean 50% mane and 50% tail but there are mixed horse and badger as well as mixed horse and boar.
But breaking in of horse largely entails getting rid of the pong whereas breaking in of boar is a more lengthy process of splitting the hair to form hooks at the ends of each hair making it softer and more efficient.
Further, the term "boar" is largely something of a misnomer: I have known newbies who think the hair of boar brushes comes from wild boar and don't know the hair comes from pigs whichj are killed in pork meat production.
Lastly we might deduce from horse frequently selling out whereas boar is almost always in stock that horse is more popular amonst shavers than boar so that demand is outstripping supply.