That familiarity is what people like and makes it good for newer players.
If they're new, then they don't have familiarity with it. Y'know, because they are new. And if you are trying to say "Well, they'll know the classic Orc", the classic Orc most people know today is almost certainly the Warhammer or Warcraft Orc, not the D&D one.
Can a new or average DM make their race as interesting as the Drow or Githyanki or the Klingons?
I mean, this is my argument? That making interesting, complex races is better to do as the publisher because the average starting DM probably won't be able to. Thus you want to make the complex one so that they can use it, or they have the option to simplify. It's much easier to start at complex and simplify than go the other direction.
Then can they repeat that over and over for every race they allow? Or just default to humans in funny suit.
I mean, they already
are humans in funny suits. They're just berserkers. Humans can totally play that: just look at worshipers of Khorne if you want humorless, bloodthirsty evil.
And what's wrong with making races less monolithic and more diverse?
That's where the monoculture comes in.
That doesn't address my last point.
Mono cultures help differentiate them from humans.
I mean, it really doesn't. It just makes them humans with a certain "hat".
Doesn't make them humans as such. But if they are sentient, fee willed etc etc they're more or less humans culturally.
This is a nonsensical definition of what "being human" is. The idea that humans have a monopoly on diversity of culture doesn't even stand up within the Forgotten Realms, where different subraces have different cultures.
Are people complaining about Shield Dwarves versus Gold Dwarves making them more like humans?
Using the same logic D&D has some bigger issues. It's a game I've had Communists gleefully loot stuff, people opposed to the death penalty quite happily execute someone.
No one thinks to hard about it. If you do there's tomb raiding, looting, stealing often murder and executions without due process.
If they're depicting humanoids or whatever as RL cultures that's a problem but if you're drawing lines between what happens in D&D to RL things it's odd when the murder, looting, tomb raiding etc is already there.
May as well pack it up you have to "not think about it" at some point. It's escapism.
Everyone's entitled to their own views it's the double think required. That's ok this isn't even if the connection is very tenuous.