"go to places like Serbia today as a black man and you'll be gawked at like you're an alien"

But don't you agree this is something we should be trying to improve, and we could do so by ensuring that movie casting better reflects the more racially diverse situation we enjoy in the developed world (who produce much content exported to less diverse parts of the world)?

No amount of seeing black characters in a movie or show (or the flipside in Indonesia, seeing non-asian characters) is gonna make it any less strange for people when they spot them in real life if the reality for them is that every single person they ever interact with in their day-to-day lives looks like them.

I also don't see what exactly you're improving here either. Most people outside of the West that I've met don't care about diversity, at least not in the way American leftists seem to portray it. In my eyes, that Hollywood cast of elites making millions off of acting are all the same type of person regardless of their gender, skin color or any of the other superficial traits people usually judge diversity by, and I can relate to them as much as I can relate to a mosquito. Likewise, I might be Serbian by blood, but I feel about as Serbian as you probably do, considering I was born and have grown up in Indonesia. I relate more to Indonesians and stories revolving around Indonesia than I do anything coming out of the West (the influence of the Internet notwithstanding), yet by all superficial standards I definitely wouldn't be considered "diverse" enough for a lot of things considering I'm just another corpse-white dude.

I guess my point is that the US, and especially the Liberal/Hollywood idea of diversity isn't anything like what my friends and I would consider diverse at all, and I suspect a lot of people in the real world feel very similarly, though that's obviously hopeful conjecture on my part. I'll take my friend group consisting of every nationality that exists (and a lot of them are dual nationalities as well!) who have white skin color over the same number of Americans of every shade of the rainbow any day of the week if you ask me to make the most diverse crowd of people possible.

I'm not I entirely agree that frequently witnessing racial diversity in movies isn't going to affect the way you react to what you might see in your own neighbourhood. Our perceptions of what's "normal" absolutely are shaped by cultural norms and they can be spread by literature, TV and film as much as they can by lived experience. I'm a bit baffled by your description of a group of friends from "every nationality that exists" but all being white skinned - how on earth does that even happen? FWIW I'm not American but I have grown up surrounded by friends and colleagues from all over the world, and they very much do have a variety of skin colours, eye colours/shapes, and other superficial features that mark them as coming from various ethnic/racial backgrounds. There's literally no racial appearance it would be at all surprising to see featured among those in my suburb (e.g. there's a significant population of Somalians, who have very distinctive features, but plenty with an obviously Mediterranean background, likewise Chinese, Vietnamese, subcontinental etc. among a slight majority from the more obviously northern European ancestry that I share). I certainly would have found the experience of going to, e.g. Japan and seeing almost nothing but ethnic Japanese quite unnerving if I hadn't had some exposure to that reality via TV and/or movies beforehand. When I do watch movies or TV shows made in the US that somehow manage to avoid casting anyone who isn't white in a substantial role it's hard not imagine that somehow the producers/casting agents felt uncomfortable about living in a multi-racial world and were subconsciously trying to project a world that only existed in their imaginations.