Exactly. As I see it such things are much more crucial for games that might look/feel dated if they come out too late. The magic within the Diablo games (especially the first two) comes from the world it places us into, the way it is presented, the music, the story.

All of these are things that shouldn't break with one year of delay. The worst thing that xould happen with a Diablo 4, would be that fans of the series get the impression it was rushed.