Radiance used to be the core item for terrorblade for along time. after s&y buff ppl started making that the core item. radiance helps the images farm faster also counters dagger when chasing. he mostly bought it for the farm part i guess, and u still get 60 damage for the main hero.
It has always been radiance skadi and then butter as a luxury item. Terror blade is mostly a hero who farms with his images. Radiance serves this purpose way better than any other item out there so theres no way its a waste of space.The best terrorblades in the world LightofHeaven, H4nni, chu etc go radiance on terrorblade and own with it.So i dont see how u can criticize this build on terrorblade.