Sorry, you are right, I really messed up the beginning of the description because it's the same as yours.
1. TV settings standard 4;3 -> the gui itself shows itself to be 4:3 which is perfecty fine, but not widescreen (black bars left / right)
2. TV set to 16:9. The gui ratio now looks bad, with everything horizontally stretched. (but no black bars)
So far, everything is the same as what you described...
Did you give up at this point? Just because the setting starts from this point.
You will then need to start a 16:9 aspect ratio TV stream and begin calibration during the video:
Setup -> Video settings -> Video calibration
The setup menu is half hidden in the lower right corner (gear icon).
The only problem is that the 576cvbs mode is not recognized by Kodi properly and thus does not save the calibration into guisettings.xml.
So after a reboot, the calibration will be lost for now. But I’m already on it to fix this bug.
A temporary solution is to manually add calibration data: