Vader cannot be compared to Ozai and Gendo.
Vader was enslaved to an incredibly powerful evil space wizard, who he wasn't strong enough to overthrow, and who also deceived him into believing that he had accidentally killed his own children when he lashed out at his wife for trying to betray him to Obi-Wan, a man who was trying to kill him.
As soon as he finds out that his son is alive, he immediately attempts to betray his master, and take his son on as his apprentice, so that they may overthrow the evil space wizard and create a fair and just galaxy, ruled together as father and son.
Yeah he was a totalitarian himself, and he was trying to bring Luke to the dark side, which entails some pretty umpleasant methods, but Vader genuinely believed that Luke needed to embrace the dark side if they were to take on the Sheevster. Not to mention his compassion for his son ended up outweighing his desire to rule the galaxy, Gendo and Ozai had no such moment.