I don’t know about having an outline for the entire ST from the start. Remember the OT was pretty much done on the fly, and Christopher Nolan revealed that his Dark Knight trilogy was done one step at a time, as they had no idea where the story would go after Batman Begins.
I think this shows that series of movies/episodes that aren’t planned from the start can work. However if you have a general story outline before you start out, it can make for a more rewarding viewing experience if you set things up and plant the seeds for story directions early on, and you’re less likely to go wrong.