I think one possible reason could be a stealth fix. The Ruby itself has a text that it proccs of RANGED attacks and Spells. I think pre-nerf the procc was happening from any attack/spell, making it equal on Melee DPS as well as casters.
Since it's a caster/range trinket, I think they just hotfixed it to work as intended and due to that it feels like a huge nerf to any melee class not using spells consistently. Could be wrong, but from the text and posts, I'd say I'm pretty close atleast.