Both mediums are reliant on writing and acting when it comes to making stories and characters interesting. I doubt anyone actually thinks screentime is related to this at all. Movies are great for telling self-contained stories, which is why they often show their weakness when adapting stories from other mediums. It's just simply not possible to capture all the nuance and details that books, television, and video games do in such a short amount of time. Which is why television is much more ideal for adaptations due to their long form storytelling that can allow for much richer character development. Regardless, a great writer can take advantage of either medium's strengths and tell equally great stories. I don't see why one has to be better than the other.
I didn't say it wasn't possible for TV series to be any good, I just said I haven't been able to find that many that captivate me as much as films do. And you're right, it has a lot to do with self-contained stories which is something I do prefer. A book is actually pretty self-contained, because you read it at your own pace and you're in control. The same goes for video games, you play it at your own pace so you're in control. With a movie, you're also more in control because you know the movie will be self-contained and its going to be over in around 2 hours. With a TV show, it's not going to be over soon, and you're not in control because its not self-contained. You have to commit much more time and energy, and the general structure of TV shows is to keep on dragging the same story over and over again (think The Walking Dead, for example). The original concept of TV shows is to keep people hooked, so in order to keep people hooked TV episodes tend to delay important information on purpose in order to make you want to watch the next episode. I find that to be cheap. Of course you can find the same tendencies in all entertainment, for example certain chapters in books tend to end with an unexpected twist that will make you wanna read the next chapter immediately. The difference here is the visualization of books is happening in your head, whereas a TV show has to visualize that 'urge' into wanting to watch the next episode.
Of course its possible to adapt books into great movies, you just have to tweak the story in certain ways to fit the format. And although there have been some costly TV shows throughout the years, in general they do not have the same budget or high level of production quality as films. Again, not saying that TV shows can't have high level of production quality, but it is more of an exception.
I think David Stewart explains it even better than me:
EDIT: Lastly, I'm not here to trash on people for enjoying TV shows. We all enjoy different things. Like if I tell someone I don't like rock n roll music, but they do, I can explain why I personally don't get the appeal, but it doesn't take away the appeal that one person gets from it.