Do you mind if I suggest re-wording part of the class, then?
I feel that this is very easy to interpret as: "If you know the spell or have its focus, you cast it normally. Otherwise, you can either cast it as a ritual or take magicaka burn to cast it normally."To cast a spell pay the magicka cost, if the spell is known or you have the spells focus the spells goes off following normal spellcasting rules. Otherwise you may either preform a ritual to cast the spell or take the magicka cost as magicka burn.