I thought it was a known fact that the Oscars is like 60% campaigning
No one is going to sit through every film released this year and categorically determine the best. Film heads, producers, critics, and actors put hours and hours promoting their work for contention. There's nothing wrong with that.
And a RT rating doesn't determine a film's worthiness for an Oscar, nor the performances in it. If Jennifer Aniston gave an amazing performance in a lukewarmly received film, good for her. Why shouldn't she promote her work, especially if its garnering Oscar buzz? As long as she isn't doing anything Melissa Leo cringeworthy, I think its fine.
That Slate article is clearly pressed for reasons that don't make much sense to me.