Was Robb’s biggest mistake not telling Edmure the plan? (Spoilers Published)

So we know that that Robb's plan was to ambush Tywin and the mountain at river run, and he wanted Edmure to keep them there and not go on the offensive. If his plan had worked as intended, Stannis wins the battle of Blackwater and Joffrey and Cersei are heads on spikes. But his instructions were extremely vague and I don't think it's fair at all for Edmure to not try and drive them off and attack the mountain when he has an opening becuase he somehow would realize that when he said "hold riverreun" he could only be on the defense.

This really seems more of like a very flawed plan by assuming that Edmure would have no flexibility with his extremely vague plan, and that Edmure MUST realize that he can never be on the attack. Without this screw up, it's likely that Stannis wins the WOT5K and Robb Stark is in a much better place. Was this Robb's biggest mistake?