The way I see it is this.
In the main lines of the Petroff, Black is holding quite well, but White has numerous tries to make something out of his slight edge, and some are more dangerous than others. Black also cannot hope for much beyond a half-point.
In the Berlin, White has serious trouble proving any advantage, the position is rich, and Black has plenty of residual chances to play for a whole point.
Nc6 or more dangerous d6 or f5 or d5