Destruction Domain: Clerics who find everything a battlefield.

[noob]

This would be broken and I've attempted to remove it from the latest version of the feature. The effect currently should apply to a single damage roll. For further commentary on this, please see discussion on the Draconic Bloodline Sorcerer's Elemental Affinity feature.

The reason it is broken is because it applies to a single damage roll.
You throw a single damage roll for an aoe spell and that is why it is strong to modify a damage roll because it affects the entire aoe.
So if you want to unbreak it make it apply not to a damage roll but instead apply to the damage taken by a single target.
Discussions about the rules of dnd 5e does not helps here: it is not because some people says "rules means that a single damage roll means it applies to a single target" that it is the only valid interpretation of the rules instead you should make rules that are not ambiguous and needing people to read a discussion of people that makes a decision about how they think the rules works.

For example I disagree that "single damage roll" means that a single target is affected by the damage roll because I did read a rule that says

If a spell or other Effect deals damage to more than one target at the same time, roll the damage once for all of them. For example, when a Wizard casts Fireball or a Cleric casts Flame Strike, the spell’s damage is rolled once for all Creatures caught in the blast.

If there is other rules that contradicts this rule then it means that depending on the table it might be one interpretation that goes or the other and it means that the power of your homebrew class might variate a lot depending on the table.
You can definitively fix it by not making something that depends on those 5e rules.

Ex: Each affected target can once during their turn deal extra damage equal to your wisdom modifier to a single target they are dealing damage to.

So that there is no need to think about the meaning of the rules of 5e and meditate for 4 hours then get a result randomly depending on the gm.
Because even for some non ambiguous things that have finally been solved such as melee weapon attacks with a weapon the way gms interprets those rules still depends on the table because it is too complicated and they make mistakes.