Whether it was a Columbus or a Chan, the introduction of diseases which the Eurasians had been swimming in for eons would have still slammed into the Americas like an apocalypse.
Even if you gave it another 300 years (after vaccines were invented) there’s no way a distribution strategy could have effectively blunted the impact. You’d need to give an additional 200 years for that to be conceivable. The odds of the Americas staying isolated for another 500 years after Columbus are nil.
My comment has nothing to do with the cultural expressions of the various groups at that moment in time. A group of Homo sapiens were cut off from the rest for tens of thousands of years for better and worse. The ‘worse’ part is that they were ferociously vulnerable to the viruses in the other population group.
“Brought together” wasn’t a phrase meant to convey happiness or agreement, it was a very literal description of two groups making permanent contact after being separated for so long. There’s not an event like that in memorable history to compare it to, as far as I know. Certainly not at that scale of isolation.