Which ratings are you looking at?
EDIT: I also checked Metacritic. True Blood is rated 68 on average across seven seasons, meanwhile Westworld is rated 75 on average across two seasons. If you take the Metacritic rating peak of Westworld (Season 1) and the Metacritic rating peak of True Blood (Season 3), True Blood is only four points ahead.
Given the difference between the Metacritic score and the Rotten Tomatoes/IMDB scores, I'd be inclined to chalk it up to different audiences. But even on the preferential platform Westworld basically at parity with True Blood, not "far south" of it.