All you’re doing here is reasserting the point I just denied. You will not find the notion that capital punishment is a “concession to the hardness of hearts” (except in the very loose sense that it would not exist in a world without sin) anywhere in the Magisterium, past or present. On the contrary it is the constant teaching of the Church from the beginning that the state exercises authority, given it by God, to punish the wicked, even by death. St. Paul taught it. Augustine taught it. Aquinas taught it. The Council of Trent confirmed it. Etc. See
this useful and measured treatment of the issue by Cardinal Dulles, no theological slouch. They all differ on the extent to which they think the state necessarily
ought to exercise that authority, but none of them deny that it does so justly.
“What God has joined, let no man put asunder”
does not apply to natural marriage, is exactly my point. Natural marriage is what existed before Christ came along. Then, a bill of divorce was permissible (he said) because of the hardness of hearts. But with Christ marriage was elevated to a sacrament, hence the permission to divorce no longer applied.
Annulment is not divorce, it is a juridical recognition that marriage never existed in the first place. You cannot put asunder what God never joined in the first place.