I don't think it's a pointless nerf. The weapon will still work for all year 1 activities, and seeing as everyone and their mom have Gjallarhorns now, everyone will still use it to DPS Crota, Skolas, and Atheon. It won't do as much damage as it did before individually, but collectively, more people in your fireteam will have it now. It would make sense to not allow it progress, honestly. Why else would they allow Xur to sell it after like 10 months of it never entering his inventory? I think it was a parting gift to year 1 players. Perhaps the best solution for the most powerful weapon is to phase it out completely. Besides, gotta give people something new to chase for all of year 2, but year 1 will always be the Year of the Gjallarhorn.