The Terminator franchise is still incredibly popular with fans, which is impressive considering that even many of those fans will tell you that most of the sequels aren't all that great. Linda Hamilton, who will be making her return to the franchise with the upcoming Terminator: Dark Fate, goes so far as to call the previous sequels, "forgettable," saying that the franchise lost its focus, something she feels the new movie will fix. According to Hamilton...
You start something and you’re invested in the franchise, but somehow the characters that you care about weren’t there. Too many people, too many story points. So I think we’ve done a good job of narrowing down the focus again so it will echo the first two films.
Linda Hamilton is of the opinion that the reason that the first two Terminator films worked so well is because the fans fell in love with the characters, not necessarily the broader mythology of the franchise. The sequels that we've seen tried to take the Terminator movies to different places and try different things by playing with the mechanics, but the original Sarah Conner doesn't think that's why people cared.
Of course, when talking about the characters that people care about, Linda Hamilton is clearly telling Variety that she means her own character of Sarah Conner. While the character made a return in Terminator: Genisys, it was with Emilia Clarke playing the role, so it certainly wasn't the same thing.
Hamilton is probably on to something with her assessment of the Terminator franchise. The first two films, for better or worse, were focused on very simple ideas and characters. Terminators get sent back in time to kill Sarah Conner and her son. Terminator 3: Rise of the Machines does keep the story that simple, but in doing so includes a lot more characters and tries to broaden and dive into the mythology a little deeper.
Terminator: Salvation then tried to be something entirely new by taking the story into the war with the machines. Again, many more characters and more focus on the the broader story. It gets points for trying something different, but if you weren't looking for something different, then it all comes apart.
It's understandable that movie studios would want to be able to make Terminator it's own "cinematic universe," though nobody was using that term back then. The more you can build on the mythology, the more movies you can make. However, it's still usually the characters that audiences make connections with, not just interesting plot elements.
Of course, that doesn't mean that just because Linda Hamilton is in the new Terminator, it's automatically going to be great. However, if the focus of the film also works in such a way that Terminator: Dark Fate also feels like it's more closely related to the first two movies, as Hamilton believes it is, then we might be on to something.