Some people say two heads are better than one. Exactly how many of them have ever had two heads though? Luckily we no longer have to rely on such dubious claims because we have Googles and Science to make a chart.
As you can see, throughout history the quality of two heads, indicated by the blue line, and the quality of one head, indicated by the red line, have remained at a constant level.
Somewhat surprisingly, that level is zero. Clearly, heads are no good at all, in any amount.
In conclusion then: two heads are just as bad as one. Heads generally are of a very low quality, and simply adding more heads does nothing at all to improve the situation.