ESS475, the main problem with your objections is that they are driven by emotions, not theology and Church's teaching. You put yourself in a position of judging what would be fair or unfair for God to do. You admitted very candidly that you know the Church teaches absolute necessity of baptism and explicit faith in Jesus Christ an the Trinity for salvation, but you question it because it is "hard to accept" and "it seems odd that America and Asia were not exposed to the Gospel" (i.e. your emotions).
To conclude:
1. No one without baptism and no one above the age of reason without explicit faith in Jesus Christ and the Trinity can be saved.
2. We can't presume that all ancient Chinese or Native Americans before Columbus were damned - some of them might have been of good will and God could have granted them faith and baptism without a missionary.
3. Those who never heard the Gospel were probably those about whom God foreknew they will reject it anyway. It is mercy, since if they heard the Gospel and knowingly rejected it their culpability and condemnation would be much greater. It is possible that God put those souls in pre-Colombian America, ancient Far East etc. precisely because He knew they will reject the Gospel, and this is why they were not exposed to it.
That does not include the mystery of predestination - God wants to save everyone and does not predestine anyone to Hell, nevertheless He does not predestine all to salvation.