I strenuously disagree with this sentiment (and it really does demonstrate that you "haven't cracked an anthropology book") for 3 main reasons-
First, as has been mentioned, "History" only covers
recorded past, which right off the hop excludes 95% of the human beings who have ever lived. "Anthropology," in stark contrast to the implications of your post, studies human societies and cultures more broadly, both of the present and the past. As someone who has spent a lot of time interacting with professionals in both fields, Historians could stand to learn a lot from anthropologists, and anthropologists have started to basically believe they're better historians. If the humanities and non-econ social sciences weren't being horrifically underfunded it'd be a really interesting time in both fields to see how those conflicts synthesize. At the very least, it is not a "substitute" but it is an indispensable supplement.
Second, a reason it's an indispensable supplement is because there are still people running around in the year of 2023 CE using terms like "primitive" and "more or less progressed" without any hint of irony or introspection. Human societies have progressed in all kinds of ways in all kinds of different directions, the concept that every human who has ever existed did so identifiably at some point on a linear, sliding scale that goes from "caveman" to "me" is a laughable assumption that nobody but the most dedicated knuckle-dragger has taken seriously in the academy since the 1950s. When anthropologists interact with indigenous peoples today, they are
well aware that they are not peering into the past or seeing ourselves in a "previous state," but, as you say, every single one of the people being studies has pretty much the same number of humans in their lineage as anybody else; and in 2023, it is nearly impossible to find someone who truly has not interacted in any meaningful way with the "modern world." Once again, literally nobody since the 1950s is out here going "now I will visit the xyz tribe and watch how our distant ancestors lived," anyone proposing a grant with that sentiment would be laughed out of any department in the world.
Finally, so yes, your keen insight that perhaps, "our" ancestors might have lived differently from modern "primitives," is not some kind of sick own of anthropology but taken as an article of faith by modern anthropologists. However, shockingly, modern anthropologists
have looked into how our ancestors lived as well. Archeology, best friend of both anthropology and history, has really grown in the last 20 years, with more and more access to technological tools to target archeological digs and glean more information from the same. And relentlessly, that information has demonstrated that our own ancestors lived
even less like us than we thought, with cities that lack a palace district (who ran the place..?) or evidence that people moved back and forth for generations
between settled agriculture and hunting/gathering (I thought once you went sedentary you never went back..?). A lot of it is uncertain and unsettled, but early returns are not supporting your suppositions.
In conclusion, you should crack an anthropology book. Strongly recommend "
The Dawn of Everything."