What kind of logic is that? I don't get it.
You say raising the difficulty was a buff because heavy horses are fast with 7 riding? But they always were! The only thing that was changed is that you can't use it at lower riding levels. How is that a buff?
As a result of increasing the base requirement to 7 riding, dedicated riders immediately get a buff to the horse, given that "difficulty" is only a minimum requirement to ride the horse. The stats of heavy horses, by and large, are unaffected.
As a result, hybrids are discouraged from using horses, while dedicated riders gain an increase in speed, agility and general performance on horseback. Prior to the patch, the minimum requirement of 5 riding allowed me to ride, but relegating me almost exclusively to infantry defense, given I couldn't ride to the other side of the map quickly enough to justify using a metal horse as a lance/couching platform.
Checking out riding on my alt with 7 riding, I found that I can actually reach the other side of the map in time to catch the last 1/3 of the spawning crowd with plenty of time to set up for a couch.