Julien - This is the D5200 review not a commentary on the GH3 and I should clarify the GH3's strong points which aren't mentioned in the article...
The mirrorless mount means you can use a wider range of glass. Have no Nikon stuff? Then it won't be a $700 purchase, to say the least.
The GH3 is weather proof and has an OLED EVF which you can use during video recording. No mirror to get in the way.
Rolling shutter is less severe.
You don't need to sharpen in post as the resolution is superb out of the box.
Battery life is miles better on the GH3.
It has more physical control, more programmable buttons and 5 dials in total despite the small body.
The moire problems are pretty minor compared to the Canon 650D.