The pitted rotor tip is usually the result of using metallic-core ignition wires instead of resistance wires. The voltage from the coil jumps a small gap inside the distributor cap from the rotor to the individual plug wire terminals. Metal-core wires have virtually no resistance, so the spark acts like an arc welder. The rotor carries six times the number of spark impulses as the plug tower terminals, so it erodes more quickly.
Jerry

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
Love your enemies and drive 'em nuts!