I think you're the one who really need to think about it. Just because you can lock up your bike with mechanical brake setup does not mean you will not stop faster with a hydrolic system. At what speed you're able to lock up the your wheels? 10mph? 15mph? and at what distance it took to come to a complete stop compare to hydrolics. For example if you can stop your wheel in 10 feet with your mechanical setup that use 160mm rotors and you switch to 203mm rotors it might help you stop your wheel in 8 feet.

Its not just because you can lock up your wheel that determines the braking power, its the distance that you can come to a complete stop. You might not feel the benefit of hydrolics and bigger rotors until you're traveling at higher speed with heavier weight.

Hydrolics are more powerfull becasue they can exert more pressure per square inch than what our hands can pull with cables. Its like power assit steering and brakes with cars. Have you ever try to steer your car with the engines off?

If you want to claim that in most mountain bike applications that mechanical brake set up is more than capable to bring you to a stop, that's fine. But to claim that hydrolics and bigger rotors will not provide more braking power and bring you to a complete stop in a shorter distance is simply wrong!