I don't think Vader cares one bit about the rule of two. Or the potential of anyone below him. Or Sith legacy for that matter.
Anyway, I liked the show. The hate comes from people who are blinded by nostalgia and don't actually want anything to change. The fact that new stuff exist is what bothers a lot of people.
I mean come on, it's been like that since forever. People who grew up with the original trilogy hated the prequels, people who grew up with the prequels hate the sequels (tho thats a bit warranted considering even Disney said they didnt know what they were doing with them). I'm certain in 15 years, people who grew up with the sequels and all these tv shows are going to hate whatever new Star Wars stuff comes out then.