[mst]

I'm sorry, but I can't leave this uncommented:

IIt's because you get with both lenses the same shutter speeds at f/2.8 or any other aperture. That's what you equivalence preachers ignore in big style  DoF is only one thing in a picture.

Right, and one other is ISO. Equivalency is about comparing the end result, the final image, and you can't ignore ISO, or to be more precise the level of noise in it.

So, in practical terms, with a 400/5.6, you'd just raise ISO by two stops and end up with the same DOF, same FOV, same shutter speed and same noise level as with the 200/2.8 on m43.