I can see what you are saying, mostly with “From Dusk Till Dawn”. It is so easy to watch this movie and see a completely different one in your mind based on the script, directed by yourself. But still, most (not squeal)movies start with a written story. Either a script that got pitched, or a novel someone wanted to bring to the screen.
Samuel L. Jackson famously said he would take the lead role just by the title “Snakes on a Plane”.
All that to say it is entirely possible to overestimate and underestimate the importance of a script at the same time.
Of course, I am not suggesting my script should be ever made into a movie — I am just having fun trying something different. Now that I’ve made peace with the idea that I am in fact a writer, I am figuring out what sort of writer I am. I figure the best way to do that is to try a bunch of stuff and see what gets me most excited.