Could you have averted the Incursions if you had gone back in time and killed Dr Doom?
The only one it could be who could do it is Dr Strange, because no one on Earth knew who the Great Destroyer was, except Stephen. My feeling is, Strange could have remembered the Time Machine from the Savage Land in Age Of Ultron, and gone there, travelled back in time and removed Doom so Victor couldn’t meet Molecule Man and start Incursions.
The only problem is the Paradox. Stephen would never have found out about Incursions unless they had already started, and if you start Incursions, the rule is, they cannot be reversed by Time travel? We reversed the destruction of Earth by the Phoenix in Iron Age HC by Time travel. We reversed the destruction of Earth in Age of Ultron with Time travel. So why couldn’t we reverse Secret Wars with Time travel by killing Doom at the appropriate time?