i have no idea about the "center of effort" but i do know that raking back depowers the boat.

There are differences in rake's effect to different boats (as apposed to the sail) due to hull shapes (asymmetric hulls acheive a bit of extra lift with mast rake) but all boats (I think) will have less available sail area with rake.

Some wind reflects off the water and hits the sail at a slightly upward angle. With less sail area up there there is less power.

Wow, it almost sounds like I have a clue…