Making the DoT useless or require more than 2 shots would almost make it's perk useless and thus make thorn almost pointless as a exotic weapon and take a slot when compared to other exotics. As much as people dislike the DoT, it's what makes thorn relevant and unique. Maybe a stability nerf or a fire rate nerf will help it, but I think the DoT shouldn't be touched aside from removing it upon the wielders death.