The emission channel is ineffective in OpenPBR material mode.

I admit this seems weird, but it is in fact the expected behavior. If you want the rest of the materials not to emit light, you need to add an Emission Color channel and fill the material with a Black Emission color.

To understand this behavior, take a light in any 3D software. You can control its Intensity/Power and its Color.
The value/lightness of its color acts like a multiplier/divider of the intensity. Regardless of the light intensity, if its color is black, no light will be emitted. If the color is mid grey, the intensity is halved.
 

The same principal is in action in Substance Painter. The Shader “Luminance” parameter acts like the intensity of the light, and the “Emission Color” channel acts like the Color of the light. Therefore, if you increase the Luminance, all your material will emit lights as long as you don’t add a Black Emission color.

That being said, I admit this is frustrating and tedious to add the channel and set its color for each Texture Set. I’ll see if we can do something about it.