I'm actually glad they aren't doing anymore origin stories. Because origin stories can really limit the story-telling, depending on the character anyway. These characters have been around for decades and decades, and it would take forever to get into certain stories if you start with an origin story. Just look at Batman for example. By not giving him an origin story, you can already introduce any story or characters like Red Hood, Nightwing, Bruce's Arab son, Oracle, etc. Hell, Suicide Squad wouldn't have been possible if you started Batman's origin story again. So there's an advantage to introducing already establish characters.
As for Deadpool, he needed an origin story. Because you needed that emotional core to balance things out with all of the vulgar humor and stuff. Especially a character like Deadpool, who was obscure to the general audience before the movie.