You sure you’re thinking of the right ARPG? Cause that couldn’t be farther from the truth for GD. Random example, look at the gunslinger build @mad_lee posted yesterday and try to tell me with a straight face the game’s all about sets and piling on item modifiers. You can cobble together all sorts of weird shit out of blues, greens, random legendaries, partial sets, sets used for the complete wrong reasons (I would know) and you’re gonna sit here and proclaim that GD dropped the ball on its itemisation? If GD dropped the ball, then most ARPGs never even had the ball, and probably don’t know what a ball is.
The case of the Shattered Guardian set is dead simple. Even if you’re not playing a build that has a lot of gear specifically catering to it, you will most certainly be able to do better if you don’t sac your amulet and helmet slot just to get +2 to all skills and a spread of resists. Being a generalist set, none of the gear pieces provide any skill bonuses whatsoever. All you get is the +2 to all. Not all skills are equally important to a given build. Getting +5 or +6 to a specific key skill for your build across various pieces of gear can be much more valuable than adding +2 to eveything. Not to mention that a lot of builds, even those short on gear will be able to make up that +2 on just the amulet and the helmet and will be free to get additional skill bonuses on the chest and shoulders. Shattered Guardian just doesn’t do enough because by being a generalist set, it can’t specifically help key skills as well as dedicated items can. You would have to be playing a piano build (so lots of skills to boost) while going into all sorts of “off” damage types for those skills in order for the Shattered Guardian to even warrant considering. And then there’s also the matter of the set providing next to no OA and DA, cause there’s almost none on the pieces and all the set bonuses are defensive in nature except the proc.