[Warhammer 40K] If the emperor had been nicer to the traitor primarchs, could the Heresy been avoided?

The Emperor helps out Angron with his slave rebellion, explains to Magnus in detail why Chaos is dangerous, doesn’t kill-steal from Mortarion, and takes the demon sword from Fulgrim. In general, he does his absolute best to avoid making the future traitor primarchs hate him.

Would that have been enough to avoid the Heresy, or was it set in stone?