Again, though what does that mean? Muhammad retconned Jesus into a human prophet. Bahai retconned Muhammad into one of many messengers, when his whole point was to be the final revelation. They are different religions. Why shouldn't they have different ideas? As for your instance with David, I'd say that's actually highly consistent with how God dealt with bad people. For instance, read the commentaries on the Babylonians. God condemns them as barbarous violent, wicked conquerers, and then has them do this to Israel. He punishes them for their war-mongering while also providing outlets for it. Just because a figure does something that assists God's objectives does not at all means he likes or approves of them. If people insist on being awful, that's pretty functional for instances when awful things need to happen.