Thorn is hated because it's lethality & range is second to none among primaries. Even if you don't score lethal damage, you've effectively taken a player out of the fight for a long time. It's range and lethality is being toned down, which is good, but it will still take players out of a fight for a long time and inflict lethal damage in 3 bodyshots, something that no legendary HC can do without Final Round or LitC so it will still be worthy of its Exotic slot.