Heroes 6 - Discussion

Technically, it was mentioned in the fifth game, wasn't it?

No. And there's no separation of damage types, except for hero magic.

And in the fourth game, defense worked against arrows; I think it was even written that way, and halfling stones ignored it.

It was written. No, they didn't ignore it because any ranged attacks were reduced.

Added 3 minutes later
In general, all these points are easily confused with features from King's Bounty.