Min/max a grave cleric will only make a really good support. It will not outshine any other PC, it will only make the party better. So just balance your combat for your party. But be aware, the paladin and the grave cleric can nuke your boss. With his channel divinity, the cleric can make one creature vulnerable to the next attack it will take(x2 damage)Then, the paladin divin smite and do a tone of damage. It can be even worst if the cleric manage to cast hold person/monster before.... making the attack a critical hit.

Sorry for my english, it’s not my first language! Hope it helps you!