The unprocessed image is fine. You can't blame the camera for your processing. To even see this supposed problem with the sensor, one has to raise the darkest parts of the image to exaggerate it, and one has to turn the monitor brightness all the way up.
By the way, ETTR has nothing to do with asking the subject to remain still. It sounds like you are thinking of HDR?
+1 I think the unprocessed file is rather good, If anything I'd be darkening the background a little to get rid of the slightly distracting drum set in the background
I think the subject remaining still thing is about shutter speed, ETTR would force a slower speed and therefore subject movement, the subject doesn't look like much of a speedy gonzales to me but you never know! isn't that what better high iso performance is for though?
@ Zim: ETTR has everything to do with the subject staying still. The point of ETTR is to allow more light to hit the sensor. A moving subject is a problem. Now, at ISO 400, choosing slower SS, say 1/60 vs. 1/125, is not really ETTR. It is just increasing exposure. It would be ETTR at this ISO only. But the reason why the ISO plays a role is ... because it is a Canon sensor. With any other sensor, ETTR only makes sense at base ISO, aside from the minor tonal differences at higher ISO I mentioned above.
@ zlatko: I tried to reveal some of the color of the background, I did not like it black. It is not important what you like or not - this is an example of banding that you said you have never seen. Now, you have.
The noise there is read noise. Higher exposure would have helped, indeed to raise the signal relative to the read noise. But with a modern sensor, higher exposure would not be needed. So all of you are saying - you should have exposed it by 1 stop more (more than that, his face would have had blown highlights, and BTW, what happened to the 4 stops?) - you are basically saying: well, you know you are shooting with a Canon, you should not be shooting as if it were a Nikon...
I wouldn't process it that way, so I would not have that problem. The unprocessed version is fine. You're taking an OK photo and then trying to add light & detail where there isn't any.
Even the processed version is not a problem. One has turn the monitor brightness up to maximum to see any hint of anything.