[Brightcolours]

Of course Oly PRO (and non-PRO) lenses can be adjusted. Actually, you can adjust AF as well, in-camera, certainly in teh E-M1, and AFAIK, in most other bodies as well.
 
Olympus does offer a PRO service as well, since the end of last year.
 
The question is whether you'd want to pay twice as much or even more, for a similar lens in FF. And please no equivalence arguments. Although equivalence wise a lens may have the DoF of a FF lens at twice the aperture number, it still is a lens at that aperture.

Aperture is a size, usually measures in mm. an 100mm f4 lens has an apparent aperture (opening seen from the front) of 25mm diameter. A 200mm f4 lens an opening of 50mm diameter. Indeed, the lens (it) still only has that 25mm diameter aperture.
 

The only reason to go FF is for more noisefree images in difficult circumstances, or for very high resolution.

That, of course, is simply not true. The only real reason to go for FF is the ability to use more shallow DOF.

However, MFT suffers much lens from banding and blotching than most DSLRs do,

That seems like, well, nonsense. Pulled out of thin air.

so from that POV up to 1600 iso and 3200 iso the cameras are easily as usable as with dslrs. In addition, IS with any of these cameras i smore advanced than any other system, so you can easily handhold shots at shutter speeds which are unheard of with non-MFT cameras. As mentioned higher up, no substitue for sports shooting (although the E-M1 comes very close), but certainly great for all kinds of images which do not have a lot of movement.
 
Kind regards, Wim