Honestly my guess is ghorn will be fine until you start getting new raid gear. Same with other 365 weapons. You'll get better stuff before then but current 365 will work fine. Looked to me like they were normalising weapons to a set attack value (180 I think) with slightly better (190 and up) available. But it is level that determines what activities you can attempt not light, so you can do a level 40 activity with a ghorn but it might not fare you as well as a ttk purple (or even blue it sounded like to me). Chances are that the decrease in damage won't be worse than being level 29 doing hard vog, which was me until 3 week before TDB came out, and I still did that raid 3 times a week teaching randoms (often level 30s who only ever pushed Templar and atheon).