The Lion Spellbook is better considering physical damage. The extra 1% physical damage is always better than extra armor defence, due to it being added as a damage percentage (more dmg received = more % protection) rather than armor defence which isn't percentage-based. Percentage points always round up, whereas a solid number can have decimals = % gives more protection.
Another thing to add is that the armor defense is just against melee attacks, whereas the physical % is against both melee and long-distance physical attacks, so as a mage that doesn't really fight in close combat the lion spellbook with the more physical % is much better.
And as a personal comment, It's hard finding good eq for a mage with ice protection, so having that 7% extra ice protection is very valuable and then you can imbue it with whatever element protection and get another 15% extra. So even if you would need earth protection, having 15% earth protection imbuement is better than the free 6% you get from the shoulder plate.