Point 1. If Mad(flt)Scientist says it you'd better believe it. He's a legend
Point 2. Vmca is a single figure, determined under standard conditions and published for certification. Minimum control speed is what you get on the day. With luck it will be lower than Vmca, but you intend to stay above Vmca anyway, don't you?
Point 3. Looking at a well known set of ATPL notes I see "Factors affecting minimum control speed: A lighter TOM reduces the element of aircraft weight balancing the lateral rudder forces.."
Dick