By Valefor.Prothescar 2013-04-21 01:31:41
On its own, blue magic skill isn't often superior to WSC boosts with recent gear options. A piece like Thurandaut Chapeau will increase D by almost two times compared to the 15 skill on Jubbah or Tayt (different slots etc., emphasis on the difference in effect, nothing more).
However... oftentimes, blue magic skill also comes with other stats, for example Mavi Tayt +2 come with not only +15 skill, but also 8STR and 8DEX. Besides that, blue magic skill serves auxiliary purposes more efficiently than base stats; increasing ranged blue magic spell accuracy, 1:1 skill:attack conversion, etc.; it has to be several tiers for blue magic skill to outright beat WSC stats on its own for a lot of recent gear options, but as a package deal it's hard to beat due to other strengths on the armors and the other benefits of adding that skill.
In short, skill tiers aren't usually chosen due to their D tier increases alone.