1) The difficulty in obtaining Year-3 Thorn has since been severely reduced from year 1. No penalty for dying in Crucible and the final strike mission is laughably easy compared to the level issues in year 1. 2) Thorn is not too strong. It is also not too weak. It is just as good as any other high rate-of-fire hand cannon. It has all the benefits of a high rate-of-fire hand cannon with an added unique perk that causes slight poison damage briefly. Your issues with Thorn can also most likely just be issues with the weapon ache-type itself. 3) Thorn inherently will never be 'balanced' so long as Crucible remains a dominant factor in weapon tuning. It's the design of the weapon that prohibits it from being anything other than terrible or extremely powerful, and exotic weapons should never hold the spot of being extremely powerful.