No it is not a good point. The cross was enough to show His love and humility. Twisting the message of the foot washing in this case was out of line.
Jesus was showing his disciples they were to be servants to the world. No one was to be above helping others. The cross brought us salvation. The washing of feet was a demonstration of how we are to interact with each other and the world. No one is above being a servant to the world, sinners and all.