Why, oh why, would a living construct have less PRR at all stages than some dude that throws on a suit of metal.
First, it costs them a feat.
Second, it is ample nerf that they have less AC for it.
Third, make wf tankies excel at something sufficient to offset healing penalties.
Fourth, uh, they are living constructs, surely they are MORE not less resistant to damage which is what this "lovely" new stat is about.
edit.Translation: The warforged should for purposes of balance, good sense, and good taste, have more PRR.