Honestly, in the case of directors who have already done 4 movies and a TV series, never. We've gotten enough from them now, so I'd rather see them bring in more new and different directors who can bring new ideas and styles into the franchise.I disagree with the notion of "giving up on doing new things" but aside from that...
Endgame was already five years ago. In a franchise that is 16 years old.
How long should they wait to bring back proven creators?
Don't get me wrong, I've loved everything they've done with for the MCU, and I'm sure their new Avengers will probably be great, I'd just prefer to see someone else get a chance.