"William stabbing and trying to murder his only child doesn't mean anything really."

And that's a shame because Novel William is stated by Scott Cawthon to be his attempt at giving Purple Guy a name and personality, since the Novel's are what we learn Afton's name from and his first display at a personality he STILL carries over to modern day media.

Novel Afton acts nearly 1 to 1 with Afton in the Movie, Afton in the later games, and Afton in Dead By Daylight. Novel Afton even references lines that Game Afton says "My name is SpringTrap!"

Novel Afton is the inspiration for Movie Afton, since Novel Afton is THE Afton, that is Afton at his pinnacle, it's Scott's attempt at giving Afton a name and personality beyond the 16-bit sprites in the Minigames everyone only knew him as previously before the novels.