That is true, Horses do cause more trail erosion than bikes, not too sure about Hikers though....
We have a few trails like that over here...... Basically, all you can do is live with it, your always going to get somebody having a rant that your destroying the trails, just think about the damage they're causing an move on, luckily we dont have this problem anymore because we found some of the best trails ion Cornwall and they're so remote nobody goes there....