I agree, but I wasn't talking about "prose." Screenplays won't teach you how to write prose or description. However, screenplay would teach you how to show, not tell, which is the essence of writing "cinematically." How to write effective dialogue instead of depending on internal monologues. How to show through action without relying on thoughts (voice-over). Also, the idea of "cinematic" writing is to put the readers inside the scenes and let them experience the story, instead of merely reading it.
There are things missing in screenplays. Sure, especially in spec scripts, which are usually rather bare-bone: descriptions, observation, POV, etc. Screenplays and novels also have different structures. I wouldn't suggest anyone to learn how to write novels by studying screenplays.
The reason why I suggested reading screenplay is that the OP said that she relied too much on internal thoughts and not external whatever. Screenplays would force her to see things in terms of externals -- may teach her how to externalize.
That said, one of the best scripts I read was The Talented Mr. Ripley, which was adapted from a novel. That script is very cinematic, yet also very literary.