Within a week I installed the first PBR airport (not FSDT) and the shimmering was back!
This tells all. We are all waiting for LM to improve on this.
We might reduce it somewhat, by lowering resolution in the normal maps, but I think this is the wrong approach, because our objects, when seen in other PBR engines, shows entirely fine, so we won't make any change to adapt to what seems a P3D4 issue which might eventually be fixed, only to change them again when and if the problem will go away.
There was a similar issue when 4.4 was just released: colors in PBR were a bit muted and shadows were too light. This was fixed in 4.5, which has more vibrant rendering and deep colors compared to 4.4. It would have been WRONG (not to mention very time consuming, for nothing) to redo all our objects, because in the time it might have taken for us to "fix" our textures that were already correct in the first place, LM released 4.5, so we would had to go back.