I get what you're saying, but it doesn't quite work that way. You can't just start with a proportional seed of 1000 and multiply from there. Travel based cases would be more additive because they don't happen all at once and they don't have the same chance of happening as time goes on. Think of it like the difference between depositing $1000 in an account returning 15% all at once versus $50//yr over 20 years. Yes, we would inevitably get more seeds,

If this were correct, we'd have to back up the date this first made it here considerably, as well as the date of first transmission to humans. China would also have had tens of millions of cases in December/January. I just don't think that's the case.

The more infectious a disease is, the more percent of the population gets it before the epidemic ends.

The problem with this is that because we don't have any built-in firebreaks to the spread - no one has been exposed before - it just moves through fast.

So, yes, what you're saying is the only way it ends...when you hit ~70% and it starts to rapidly run out of targets. The best way to do what you're describing is with a vaccine..