[Brightcolours]

I of course agree with you on that usually equivalent lenses are similar in size/weight. But with tele lenses a smaller image circle may enable smaller back elements, front elements remain more or less the same for the apparent aperture to remain the same.

However, if shallow DOF is not a want, and you just look for a vacation snap thing with a big FOV range and will use small apertures anyway, MFT offers lenses with smaller apertures and so will have the size advantage. This also applies to that Leica 100-400mm you brought up