X20 Sensor, This is News

That's an interesting observation - yes, I guess only time will tell.

It would certainly seem to be something of an oddity - in that, at ISO200, the exposure is obviously only getting 50% of the light of an ISO100 exposure.

Looking at it simplistically, therefore one might expect the image signal's shot noise to be some 40% higher - which really doesn't seem like a good starting point for what is still a relatively small sensor.

Arguably the 'quantum efficiency' (efficiency of photon capture) might be better than the previous sensor - but it couldn't possibly be enough to compensate (i.e. would need to be 100% better).

One possible theory/explanation may very well be...

In the absence of the previous sensor's 'EXR-DR' dynamic range capability, it may have been deemed more desirable/necessary to lower the average sensor exposure level (by increasing base ISO) in order to provide an increased proportion of highlight headroom.