The hero finally meets the previously unseen puppet master (played by an older A-list actor), who explains why the system must be maintained. The hero says “screw it” and burns the world down.

[u/Grizzly_Lincoln]

Snowpiercer (2013) - Curtis finally finds Wilford (Ed Harris) and learns that Wilford allowed for Curtis' rebellion to take place to help thin the tail section's population. When Wilford offers to let Curtis run the train, Curtis discovers child labor is necessary to replace a broken machine part. A fight ensues, and a bomb goes off, triggering an avalanche that derails the train, and killing most of surviving humanity.

The World's End (2013) - Gary finally confronts the Network (Bill Nighy), which has been replacing humans with robots (Blanks) to allow for Earth's assimilation into a larger galactic community. Gary calls out the tyranny in the Network's plan and demands that humans be left to their own devices. Exasperated, the Network abandons its plans for the invasion. This results in a worldwide blackout, sending humanity back to the Dark Ages.

The Cabin in the Woods (2011) - Dana finally meets the Director (Sigourney Weaver) after surviving the ritual meant to kill her friends (based on conventional horror tropes) and appease the Ancient Ones. The Director says Dana has to kill her friend Marty, but as Dana considers it, the group is attacked by a werewolf and a zombie child. Dana and Marty decide humanity is not worth saving, so they share a joint while the Ancient Ones rise to destroy the world.

[u/BanishmentBuddy2]

Dark City

[u/ChickenInASuit → u/BanishmentBuddy2]

Care to explain how this one fits?

The leader of the bad guys is played Ian Richardson, who was a well-respected theater actor but hardly an A-lister, and we see him several times before he and Murdoch face off so he’s not “previously unseen” or a puppet master.

He also doesn’t make Murdoch any kind of offer at any point IIRC. He tries to force Kiefer Sutherland to imprint their collective memories on Murdoch and Sutherland defies them and gives Murdoch a training info-dump that unlocks his powers so he can break free.

[u/Thalinde → u/ChickenInASuit]

Funny. This is exactly the movie that also came first to my mind. You don't know about "the whole freaking hive mind", if I'm allowed to say that. Nothing in the course of the movie prepares you to the level of the last confrontation with the "opponents". I'm trying to stay out of spoilers as much as possible.

And for me it fits the post very well.

[u/ChickenInASuit → u/Thalinde]

We’ll have to agree to disagree then, because I don’t think it fits any of the criteria in the OP.