"the mainspring transfers Energy to the hammer and Since the hammer is lighter their is a more efficient transfer to the firing pin."
Uhm... Not sure what you mean by "efficient," but those who say you can compromise reliability are correct.
Think of it this way... A bowling pin match.
The bullet is the hammer, the bowling pin the primer.
A heavier bullet at a slower velocity (such as the .45 ACP), is usually MUCH better at taking the bowling pins off the table than a lighter bullet at a higher velocity (such as a 9mm).
By the time you raise the velocity of the light bullet high enough to compensate for the loss of momenum (IF you can safely raise it high enough), you've got recoil that's tough to handle.
Similarly, in the revolver, by the time you raise hammer speed sufficiently to counteract the loss of momentum, which you have to do by increasing the power of the main spring, you've got a trigger pull that's hard to handle.