I’m late to this party, but here are my two cents.
I often find that the problem with “the formula” is when it becomes a distraction. If the reader can guess what is happening before it happens, not due to good foreshadowing, but due to overreliance on cliche, then it can break the suspension of disbelief. This can be problematic to work with, because even if the ending breaks with the formula, if everything up to that point hews too close to the formula, then the reader may give up because they think they already know how it ends.
Not necessarily. One of the most interesting analysis I’ve ever seen in my life was about the first Avengers movie, and how it (and almost all of Marvel’s movies) was basically made to disprove that point.
What’s the plot of the Avengers? Bad guy steals mcguffin, good guys try to band together to stop him, good guys argue, bad guy tries to kill them, good guys put their differences aside and smack his head into the concrete. What’s the plot of Guardians of the Galaxy? Bad guy wants mcguffin, good guys try to band together to stop him, good guys argue, bad guy tries to kill them, good guys put their differences aside and smack his head into the space concrete. Both of those were massive blockbuster.
Why where they so successful and (but that’s up to personal taste) so good? Because in both of those stories, the plot was never the main focus of the director. EVERYONE already knew what to expect, down to the happy ending, and that’s the disadvantage of working with some source material (there’s no way they’d kill a character off). But this way they could focus on characters, on making them relatable, on making sure that every single one of them was interesting and memorable in his own way. Dialogues in the Avengers were clearly written by someone that knows a thing or two about characterization. Plus, you know, big space battles and stuff.
Basically, what he said was that it’s not important the direction the plot’s going in; even if you can already imagine the ending, if the journey’s enjoyable, people are still going to love it. Not everything needs to be revolutionary to succeed.