This is an interesting argument, because it’s worth considering, for example, the Australian Aboriginee.Are you saying they wouldn’t have improved on their own a couple hundred years? Who knows what would have happened. But I’d take my chances over decades of rape and murder and loss of culture.
Consider their level of technical developement when contacted by outside cultures. They hadn’t just been outpaced by the era of sail, they’d been outpaced by the era of archery.
How long exactly do you think it would have taken for them to get there? If they had of been left entirely alone, do you think they’d have alloy metallurgy by now?