There is no way to play out a full story by splitting the screen time for 3 stories. Even splitting it for 2 stories is not a good idea. By splitting the time that many ways it’s basically impossible to really flesh out a story and add depth. In a one hour episode you really only get 40 minutes of air time. If you split that for two stories you get 20 minutes of screen time to tell a story. 3 ways? Yeah now you are just wasting a show. You only get 13 minutes to tell a story.
Combine the above with the fact that we have less and less episodes per season, and This creates a real problem to tell a story of any sort
I feel like you’re pertaining to a specific TV show. Which one is it?
While I agree running multiple stories in parallel can get problematic, it all still boils down to execution. 3 equally important stories might not work with a limited season, but a proper balance of storytelling and good execution of the intersection of the stories at the midway or climax of the season can still work.