> At even 2.5% annual population growth rate a population recovers from a 90% population drop in under 100 years.

Then the population growth was obviously lower than 2.5%. That was partly due to European oppression of course, although the worst (U.S.) American crimes against the Indians didn't come until the 18th and 19th centuries (the Indian Removal Act/Trail of Tears being a particularly notorious example.)

No-one disputes that the overwhelming majority of the pre-Colombian population of the Americas was killed by infectious diseases in the decades immediately after contact. Jared Diamond is just one anthropologist who puts the figure at 90%. [0] It took the population of Europe 200 years [1] to recover its previous levels after the Black Death killed "only" 30 to 50% of its population.

If you read Diamond and Mann, there are some interesting explanations for why Native Americans were so susceptible to European diseases, much more so than in the other direction. Two big factors were that 1) Europeans had spent centuries living in much more densely-populated, interconnected, dirty and unhygienic towns and cities, so they'd already been exposed to more disease and thus had more immunity (although not total immunity as I'll discuss below). And 2) Native Americans were descended from a very small number of people - possibly just 4 or 5 waves of a few hundred people each - who originally crossed the Bering Strait from Asia, and this ancestral bottleneck meant they had far less genetic diversity than Africans/Euarasians, meaning that if a disease could kill one of them it could likely kill very many of them.

(Incidentally, syphilis is thought to be one of the few diseases that travelled the other direction in the Colombian exchange, i.e. it's thought to have originated in the Americas then spread to Eurasia.)

> So, native populations should have had time to develop immunity to European diseases.

It's not really that simple; diseases like smallpox were devastating all throughout history, even after thousands of years of "time to develop immunity". Many, many European settlers of the Americas were killed by smallpox epidemics; just go to [2] and ctrl+F "smallpox". What neutralised the threat of these diseases was vaccination, which didn't become widespread until the 20th century. We're so used to living in a post-vaccine world that we forget just how commonplace and devastating infectious disease used to be to all populations everwhere. (Although, of course, the events of the last year have helped to remind us.)

[0] https://www.pbs.org/gunsgermssteel/variables/smallpox.html [1] https://www.ancient.eu/Black_Death/ [2] https://en.wikipedia.org/wiki/List_of_epidemics