
Ravingdork |
Pathfinder Roleplaying Game Superscriber; Pathfinder Starfinder Roleplaying Game Subscriber

This is common among many alignment-restricted classes/prestige classes. Some are simply...more forgiving...than others.
Basically it's the Jedi/Sith changeover trope. The Jedi doesn't grow weaker for becoming a Sith. He can still do everything he could before being tempted to the dark side.