Well, obviously lighting is a force ability you can learn over time. So why assume only one person throughout history could do it?
Obviously swimming really fast is an ability you can learn over time, so why assume only Michael Phelps is the only person throughout history to win 23 gold medals in swimming?
Answer: because it’s really, really hard.
Marc Macguire broke every one of babe ruths records. So someday there may be someone that breaks Emporers records. Maybe in those bad 100 years there were sith lords that knew lightning attacks too.