Opinion on Inevitable Events

This is partly inspired by Romulus Augustus' TL, which seems poised to end on a sour note given the coming Justinian plague. However, the POD for the TL was in the 470's decades upon decades before the plague OTL and so should it not be averted, at the very least slowed down?

My question isn't about the TL, it's only an example. Why are POD's considered outside the realm of human control treated as fixed points that must occur? If you start in 1000 AD, and play everything from there should you not have a different outcome from OTL or are there still going to be rampaging Mongols 200 years down the line no matter the changes.

For me events caused by humans always butterflies away. So if POD is on 1000 AD, Mongols, leastly on this form what we know, should butterfly away. Disease epidemics too probably butterfly away. Some events caused by humans are inevitable, for example foundation of Americas. Of course this happen very different way and might happen earlier or later. But it not be possible that foundation of Americas not happen before 20th century.

But geological events are probably pretty inevitable. With POD 1000 AD you might be still earth quakes and volcano erupts which happened centuries later. For example if POD is during Napoleonic Wars there might still be South Asian tsunami on 2004. Same things is with meteors. Not matter with POD there is probably still Tunguska Event.