"So if I'm understanding you, what you're saying is that my overpowered headlight has damaged the power wire, which is kinda deactivating the fuse, and that in turn may have fried my ignition switch?"
The fuse is designed to be the weakest link in the chain. To melt the fuse means that circuit (in this case the Main fuse circuit) was subjected to over-heating. The ignition switch is the first component down line from the fuse and the contacts inside the switch are sensitive to failure due to heat and electric arcing. Once the fuse melts that circuit is dead and no additional damage can happen after the fuse. If the switch was burned it would be during operation of the overloaded circuit.