While, as a GM, I resist offering this kind of advice, if you were familiar with Cleric spells you would keep hammering the Cleric.
Some facts you might not have inferred:
He's demonstrated that he can cast level 1 spells, he must be able to cast at least 3 per day and so far he's only used 2 (Cure Wounds and Guiding Bolt), which means he has at least 1 Cure left (which would really set you back on the demonstrably hard to hit armoured guy) or he could use another Guiding Bolt (which will almost certainly lead to a PC KO -- it's 4d6 Damage and the next attack on the target has Advantage. That greatsword also hits like a truck).
This last round he cast Guidance on the big guy, which gives the big guy a d4 he can add to any one attack roll after rolling. Cleric PCs are pretty good, but Cleric NPCs are really good (because, since NPCs usually die, they tend to burn ALL of their spells in the course of a single battle; while PCs spread out the good stuff over several battles by necessity).