When equipping Trang-Oul’s armor and gloves on my Sorceress, the +18 Fireball set bonus only adds +8 to the Sorceress’ Fire Spells tab, and nothing under the Item Skills on the General tab. When equipped on Barbarian it appropriately added the +18 under Item Skills on the General tab.
Thats how the game is design. O skill equip on original character doesn’t boost as much as others.
Example equip CTA on Barb, hustle on Zon