최대 레벨이 100까지이고 업그레이드 가능한 레벨 범위가 5 만큼이라는 것 같네요.

예를 들어 80레벨의 아이템을 드랍하셨으면 85레벨까지 업그레이드 가능한 것입니다.

자문 자답이네요 14일에 열리는 새로운 시즌 정보 찾다가 발견했습니다 ㅜㅜ

Crafting has been revamped to give players a better access to useful items while not being overly complicated. Therefore, the number of crafting materials have been reduced, and the Tech Tree has been altered as well.

• All crafting times have been removed so items are now instantly created upon crafting them.
• The blueprint system has been altered. Old blueprints have been removed, and numerous new ones have been added. 
• Crafted items create items based on player level.
• Relic items can now be crafted occassionally via the Crafting panel.
• Fusion is now the name of the feature that allows players to fuse sockets onto an item.

처음부터 item level upgrade 가 아니라 fusion으로 찾아봤으면 바로 알것을...