The lens drives these concerns, yes, but the pixel size still has significant impact. If I build a lens that will cover a hypothetical 16MP sensor with good qu

The lens drives these concerns, yes, but the pixel size still has significant impact. If I build a lens that will cover a hypothetical 16MP sensor with good quality over the whole sensor, it will also cover a hypothetical 16MP sensor of half the dimensions. However the smaller sensor demands a higher optical resolution (line pairs / mm) than does the larger to resolve those 16MP with the same clarity, and so the smaller sensor will deliver lower effective output resolution (again, in terms of resolvable line pairs) than will the larger sensor given the same glass. And if I'm searching for shallow depth of field, again the larger sensor has inherent advantages. Physics isn't your friend once you start trying to build arbitrarily fast small sensor lenses to replicate what's easy with a larger sensor lens. I'd be delighted if these concerns weren't true; my m43 camera is much lighter to cart around than my FX one :) And yes, we can now get DR and noise performance from a smaller chip that we used to not be able to with a larger chip - but there are definite advantages still to the larger chip that won't go away.