GHorn has never been needed for anything but it's also not accurate to downplay how much of an outlier it is. I've always wanted to add up how many WP round hit markers there are but it's hard to keep track of them all frankly. The WP tracking also means they consistently do damage unlike Cluster bombs which miss quite often unless the target is stationary. One Horn does more damage to Minotaurs than a Truth even with the Void shield.
There's always been backlash against GHorn, especially by people who didn't have one or resented feeling like they "had" to use it all the time. We've been having the same conversation about Hezens Vengeance, Hunger of Crota, Truth, Dragon's Breath and every other exotic weapon or rocket launcher since week 2. Of course player skill is the most important factor but GH is a huge outlier, both for DPS and the ease of applying that DPS.
Only BHam can achieve or exceed its DPS but it's much more situationally limited. With GH, I can jump all around the Skolas arena firing off shots in a split second that will track their target and do full damage. I've done plenty of Skolas Schools where I had the only Horn but I'm always relieved when at least one other person has it. I've never required it for any activity but it's also the only PvE weapon that makes such a noticeable difference.