I find that starting new projects with multiple people right away is almost always a recipe for disaster, or at least drastically reduces the potential quality of the project before even writing the first line of code.

Maybe it works for small projects or teams of mostly junior developers. But for anything remotely complex I can say from experience the architecture won't be ready in a few meetings but rather after much hammock time.

That architecture will then become a main factor in your productivity, maintainability and performance. These 3 are very, very hard to optimize for once the architecture is in place.

Other than for code reviews or mentoring junior developers, I've never seen pair/mob programming works with quality results. Its nearly impossible to solve complex problems when outside the zone, and its nearly impossible to get in the zone in a pair/mob setting.

That makes it sound like the whiteboard session is much better. Cause there's planning involved, instead of just throwing some code together.