The problem is viewing it as a sci-fi action movie (which I’m assuming is how you viewed it), because that comes with its own connotations. Blade Runner is more like sci-fi noir or neo-noir. Action and noir can be on the opposite spectrum when it comes to pacing (that’s been my experience, at least). The action is how it is because it’s not trying to be flashy. That’s not its purpose, and it’s not that kind of film.