Would it be fair to say that the fact that it was an entire package of diseases that all arrived pretty much at once that compounded the damage, more than just the sum of the parts?
For example, say that small pox would kill 10% of a population, measles 10%, and influenza another 10% (purely demonstrative number there). All of them arriving at once would likely kill more than just 30%, I would imagine. Correct presumption?
In general yes, but the percentages are simply mind numbing.
The death rate could be dramatic, and there was no knowing in advance. As an example, Cuba lost 1/3 of the the entire population to smallpox in 1519, a measles outbreak a few years later took out 2/3 of the survivors, leaving only about a quarter of the pre-contact population alive. A few years later, these survivors were effectively non-existent, having been finished off by further illnesses and the general abuses.
Overall perhaps as few as 5% of New World populations survived the Colombian Exchange.