Thanks for the call out! There are definitely companies that go with (A), but in all the companies I've been at, (B) is the model.

As others have responded, there are definitely trade offs with different models. The way I've seen (B) worked well is:

* Given a project, separate out the "level" of different axes. A project could have level N technical scope, but level N+1 collaboration scope, etc.

* Let the level-N engineer handle one level N+1 axis at a time, with supervision on other axes.

* And if they ace one axis, then back off and give them more responsibilities on the other axes, for the same project or subsequent projects.

Of course there are also scenarios where someone is just thrown into the deep end. They will either sink or swim :)