“They fail to realize that sooner or later someone, probably the Chinese would have come.”
Well, if Columbus hadn’t come, the Portuguese would still inevitably have discovered and colonized Brazil just a few years later. They had a colony on Cape Verde, which is directly between Africa and Brazil, they were sailing regularly up and down the coast of Africa, and they were using new sailing techniques that involved sailing away from land and into the Atlantic to take advantage of the Trade Winds. So combine those three facts and the Portuguese discovering Brazil becomes just a matter of them rolling the dice enough times to get lucky.
Indeed, in the year 1500 a Portuguese explorer on the way to India was blown off course and landed in Brazil.