The fundamental problem with your question is the perception that there are these prescribed stages of development and each stage is an advancement on the previous.
Instead, the indigenous peoples in the world were just as “advanced” as the colonizers who slaughtered and enslaved them. They were not on different stages of a tech tree like in a game, they just developed different societies.
So of course slavery was not necessary because there is no such thing as necessary advancement. Even if you argue that advancements in medicine requires more modern modes of production, places like Cuba or the Soviet Union skipped or sped through or skirted around or limitidly used Capitalism and still developed incredible health programs. So then capitalism isn’t even necessary for technological advancement in that way, let alone slavery.
I’ll agree about the rigid format of movies but to say that’s why I think movies have the greatest impact on me of any media.
A movie is a very tightly packaged combination of art forms that has to hit all the right brain pieces at all the right times because they have such a limited amount of space to do it in.
The greatest movies are those that can keep you completely focused for two hours and affect you for days after. They are able to masterfully execute on all art forms at once.
Even for great books I generally read them in multiple sittings which at least temporarily takes me out of their world. Games are an even greater collection of arts in that they also add an interactove element, but they’re often so long that I never quite get fully into the stories. I ran into a soft-lock in Disco Elyseum that caused me to have to re-load a save and redo some pieces. That experience isn’t too uncommon in gaming but it’s something that would never stand in a movie.
Basically I think the greatest movies are those that manage to affect me so so much with such tight constraints.