Legendaries are being balanced against each other, so the ones that give the DPS increase all give relatively the same % increase. If A was giving 50K DPS increase which is 20% increase to spec X and B was giving a 50K increase which was a 10% increase to spec Z. Then based on their ideal % increase they want Legendaries to give, Either A or B is going to get nerf/buff. The tuning changes had noting to with how high or low a spec was performing, it was based on the items giving to small or to big of a gain over their intended goal.