Taken to the extreme (the same extreme, I suggest, as "if we have Hero Points, the players can auto-succeed at anything and override the entire game"), this says "your characters live or die at the whims of the GM - maybe he spares you a TPK you earned, or maybe your hard-won victory turns into a TPK".
At one extreme, we have a story written by one or more players. At the other, we have a story written by the GM, in which each PC is expected to play their scripted part (but you can ad lib in non-crucial elements of your role). Between those polar opposites rests a lot of possible divisions of authority and agency.
The GM lays the plot, sets the scenes. He is not the "first among equals" at the table. It is his game/world.
The characters parts are completely ad-libbed. Tell me you've never been in a game where the players went so far afield that they weren't even remotely close to whatever rails the GM may have laid.
Now, as an experiment, get 9 friends around a table and give each a pad of paper. Each person writes one sentence and passes the pad to the right. They read what is written and write another sentence. And so on and so on, until the exercise is complete. When you're done see how many of those "stories" make any kind of coherent sense from start to finish.