As someone who studies history I will say this:
1. The Native Americans were not the saints they are often made out to be by leftists. They fought wars among themselves over territory and resources the same as every other tribe, people, or nation on the planet. Powhatan intimated to John Smith that he had built his confederation of tribes through conquest.
2. The relations between the early settlers and the natives were much more equal than commonly supposed. The Pilgrims and their near neighbors often played referee among the various tribes who lived nearby in hopes of keeping the peace.
3. The natives adapted to the societies of the settlers around them, often effectively to the point where there was not much difference. Joseph Brant, an Iroquois chief in the 1700s lived in a house that had glass windows. In researching my own family I believe the first ones who had glass windows might have been in the late 1800s....
4. Let’s just take a historical supposition. Suppose, instead of white Europeans, the Mongols had somehow come. Genghis Khan and his ilk. Does anyone rationally suppose the lot of the natives would have been better? I think rather that the whole of their culture and people would have perished from the earth, fighting against people who were ruthless enough to kill all male children taller than a wagon axle. My point is they could have come out a whole lot worse.
Suppose even if the Chinese fleets of the early 15th century, which certainly reached Africa and maybe explored the Coast of North America (they certainly had the capability), had colonized California. Would the natives bee treated any better than they were by the Spanish when they came in the 1770s? There is an effort by the Left to demonize there Europeans and to romanticize the Indians. But California before the Europeans arrived was no eden.