A critique

In the finale, Booth does all the fighting, gets stabbed, kills two of Manson's clan outright, and mortally wounds the third, who staggers into the pool and would have drowned, at which point Dalton, in an over-the-top fake Hollywood manner (as opposed to Pitt doing it with his fists and his faithful dog) burns her to death with a flamethrower. Significantly, the flamethrower itself was leftover from a movie. Even when Dalton does something heroic, he does it in a fake way (killing someone already dying) with movie props.

As he did at Spahn Ranch, Booth calmly wins the day through natural toughness and ability, after which Dalton fools himself, and others, into believing he also saved the day, using outlandish movie props in the process. It’s the Spahn Ranch/ Western movie set dichotomy from earlier in the film all over again.

And then, of course, Dalton is given all the credit. He ends up relating his heroic tale to Sharon Tate and her friends while Booth is being taken to the hospital, and the film ends with Dalton being granted entrance to the New Hollywood that had previously shut him out, and leaving behind the Old Hollywood, and the best friend who gave him access to it.

By this, I don't mean he was personally abandoning his friend. I mean that as Booth was being driven away in an ambulance, having suffered from an injury that would almost certainly end his career as a stuntman, Dalton was finally being allowed "behind the Green Door," and was on the cusp of starting a new acting career, one that likely wouldn't require a stuntman. He'd still be buddies with Booth, but the days of "them against the world" are over, and Booth will go back to his meager life in a trailer, while Dalton will live among the New Hollywood elite.

There's also a clear implication that moving forward, Dalton is going to be performing in more modern roles. No more westerns or retro action flicks that require a stuntman, but rather films like Polanski made-- psychological thrillers, crime noir dramas— films that require the acting chops he was able to channel in the earlier scene, with the child.