Avec les courbes pouvoir agir que sur la luminosité et pas en RGB comme chez vos concurrents

I don’t use DXO, so I’m not sure what the L function does.
Luminance? If so, it does the same thing as in the two screenshots I posted from Camera Raw.

With the curves, choose to adjust only the brightness and not the RGB as with all your competitors.

If I understand you correctly, you want to adjust the brightness of the whole image, not individual RGB channels.
There are two ways you can do this in the Curve panel.