I know A LOT of players are saying stuff about this but what i do know is that a lot of runes are mostly used for crafting i.e. enchanting, so what if the "rune" is actually a destruction spellbook?
Much like the staves which are two-handed magic weapons, spellbooks will be one handed weapons while still possessing the elemental properties but with NO tanking properties,
Fire=Single target benefit
Lightning= AoE benefit
Ice= Bonus damage against chilled foes and DoT benefit
I would think that many of the abilities from a skill-line like this to mainly have your character imbue their weapon with magic, based on which element of spellbook you have equipped
and unlike shields which have other styles based on themes, spellbooks will have styles EXCLUSIVE to them with the books being more ornate. Novice, apprentice, adept, expert and master
and of course the light/heavy attacks from the thing will be magic based cause your fusing magic into your weapon to attack. It makes more sense too because other characters in games have paired their weapon with a spellbook, ex: robin from fire emblem and the vestal from darkest dungeon