Having a single power line plugged into a receiver can't deliver as much power as two leads plugged into two ports on the receiver. A single power wire into the receiver can't handle a constant 7.5 amps.
I understand what you are saying, you're just wrong.
You are suggesting that the airplane won't run on one battery. IT WILL.
And yes, those wires are rated for more than 7.5 amps. The bus on the receiver is rated for 20 amps.