While I think this is a good point, I think it neglects to consider the sheer level of productivity, both from an operational and output level, that Universal must contend with. Netherworld may have a stronger haunt, but it has a smaller space, and a single attraction to deal with. And I'd be surprised if their traffic is anywhere near what HHN sees (although I'm sure it's quite impressive). Netherworld and its ilk are the exceptions though, not the rule. Whenever you see a special haunt documentary, or anything about the top of the line haunts, it's always the same 6 haunts (Darkness, Netherworld, Headless Horseman Hayrides, etc...).
But they aren't indicative of your average haunt. Far from it, in fact. As I said, the vast majority of haunts use the same tricks and tactics, and aren't all that impressive (I've been to a fair number of them, both seasonal and year-round). And they have the benefit of smaller scale and scope, so they can be more focused. I can't say definitively, as I haven't been there, but I have to imagine that not a whole lot changes from year to year in terms of content. HHN, on the other hand is 95% new each year, with generally only some repeats of props or costumes. I think it's very unfair to come down on HHN for some of this stuff, when the park is not a dedicated haunt attraction, and has to look at much higher volumes, along with the constraints of putting things up and breaking them back down easily and quickly. I'm sure the budget for HHN is not what it is for the top haunts, percentage wise. Or at least, it can't be allocated the same way the top haunts in the country allocate theirs.