Might & Magic X: Legacy

In the 6th game, aren't they un-upgraded and still wearing armor?

I don't think so. But the main thing is that their helmet is completely in the style of the 6th game; there's nothing like that in the 5th game at all.

I don't remember the models from the 5th game very well (I last played a couple of years ago), but it seemed to me that they were brought up to the general level.

Well, that's five minutes in Photoshop, you know. The models clearly weren't changed; only the textures, maybe, were made less contrasting.