Q:
unused offensive vs unused upgrade slot
A:
Firstly, ascended items already have the stats from inscriptions/jewels in them. So the Ascended ring already has the stats from the exquisite jewel you wanted to add (or at least another exquisite jewel)
Secondly, Ascended items can only accept infusion which are offensive, defensive and utility. That’s what the name of the slots are for so you know what type of infusion you can put in it. And the only Ascended items with Utility slots are Amulets.