Do the War Domain cleric's War Priest feature and Two-Weapon Fighting's second attack both use a bonus action?

Question

One of my players is a War Domain cleric and dual-wields weapons. He's been making three attacks:

1. the Attack action
2. bonus-action for the other hand, from Two-Weapon Fighting, and
3. use one of his "War Priest bonus attacks" (PHB, p. 63) for the third attack

But as I'm reading it over again, I've just realized the War Priest feature says that it is used as a bonus action.

Since this "bonus attack" is used as his bonus action and an "other hand" attack from Two-Weapon Fighting also uses his bonus action, does that mean he only gets one or the other?

He specifically chose the Dual Wielder feat (PHB, p. 165) because he wanted to "slice and dice". I understand that the "War Domain bonus attack" is meant more for a sword-and-board or 2-handed weapon, but would it be unreasonable to allow him to use that "War Domain bonus attack" (of which he gets 4 uses) as a third attack from time to time?

Answer 1

Correct

You only get one bonus action to use on your turn. You can't make a dual-wield offhand attack and use the war priest ability in the same turn.

As for unbalanced? If they were using a two-handed weapon they'd get the most damage from a greatsword or maul which would do 2d6 + strength modifier per hit. So if they hit with both attacks they'd do 4d6 + 2 × strength modifier per turn.

For dual wielding the best you can do, given the dual wielder feat, is a pair of 1d8 + strength damage weapons. That would give you 2d8 + strength modifier × 2 max damage per turn.

Now if you consider the combo you are suggesting you could do 3d8 + strength modifier × 2 max damage per round. That is slightly less average damage per turn than the two handed combo given by a greatsword/maul and war priest attack.

In terms of damage then it isn't really unbalanced. The number of attack rolls is a slightly different matter. One more attack roll per turn increases the odds of a critical hit on each turn slightly. Instead of two attacks, each with a 1 in 20 chance of a critical (assuming nothing else is affecting the range of values), you have three attacks with the same odds. Not huge, but significant. It also increases the odds of a critical miss but you are pretty much never going to hit on a 1 anyway so it doesn't really a difference.