When upping your grimoire in your off hand, you should still be able still to block/parry if you have a sword/staff/etc in your main hand. They’re tied to the same button/key, but cancel each other out which feels strange since they are different hands.
If I am looking at my book I’d probably hold my sword in front of me for protection, only downside of spellblade is losing blocking, doesn’t make much sense imo