There is no need to make leveling an alt or friend difficult. If someone has already gotten to the cap and wants to level an alt fast and gear them the only way to do it at the moment is the same way you have done with your original character for the most part.
My suggestion is to make the distance to get exp longer so people can leave their alt afk near the combat but not directly in the combat. No one really likes the leveling and its just that more tedious leveling a second character and for no reason either.
Also to add in increased levels at which you can gain experience maybe -5 and +10/+15 levels difference.