How exactly were you using the Corona Output map?
Generally it is intended for making a texture independent from VFB tone mapping. So if you increase exposure, the exposure of the bitmap will remain at the same level regardless of that. The typical use here is setting up a background visible behind a window. You can then increase the exposure to make the interior brighter, and prevent the background image from becoming overexposed.
If you plug it into the diffuse channel, it will behave the same way.
If you plug it into the self illumination channel, it will display the texture as "glowing", but will still consider the diffuse color and level. Maybe to fix your issue you should simple set the diffuse color to pure black? (or diffuse level to 0)