Destruction Domain: Clerics who find everything a battlefield.

[Breccia]

This is actually intentional.

Well okay then.

4e allows attacks to target Will instead of AC by default, and this is based on one power that does so.

Yes, but you could boost your Will defense. It was still something you could do to defend against this kind of attack. 5E doesn't have that.

Would it work if I changed it to a wisdom save that forced the target to take damage and then be charmed by you until end of turn (on top of the extra attack)?

I mean, I still think it would be better off replaced, but forcing another creature to take an action sounds like something that should require a Wisdom saving throw. Just ask yourself "what if I, the DM, used this on the party?" I imagine a lot of players would be irate at being forced to attack their fellow party members with no way to stop it. Again, I can't think of any compulsion-style effects in 5E at all that don't allow a saving throw, mostly Wisdom. It would also assumedly add "creatures immune to the charmed condition are immune to this" which I'd also appreciate.

If you require a successful attack, I'd recommend allowing the Cleric to use the ability after they know they hit. Otherwise it's too restrictive again. Adding charmed for their next round seems fair, it's a mild add-on but the Cleric is in melee and would appreciate the breather.

I mean, it kind of is misfiled from a Leader class. So I'm trying to thread the needle between "clearly destruction," and "clearly runepriest."

Right, I don't have a problem with a Striker/Leader at all. Striker/Leader with a dash of Controller starts to feel overseasoned.

You've addressed my concerns, I'm curious to see what you'll end up with. Again, the subclass overall feels pretty good. They'll have fun running with the three reavers we've seen in the last week :D