I disagree.
First of all it appears your definition of exposure is how light or dark an image looks on whatever medium it is on. That's fine, many people have that misconception and we live with that.
When I set exposure* the final image lightness is not even a consideration at that stage. I set the widest aperture that gives my DOF and the slowest shutter speed that meets my blur constraints without clipping important highlights. The camera can set ISO wherever it likes as long as important highlights are not clipped. I set the final image lightness in post.
This way I have maximised the exposure* for the photo I want and maximised the quality of the raw data because the SNR has been maximised.
I don't need a triangle or any other shape to maximise the quality of the raw data.
* exposure - amount of light that struck the sensor per unit area while the shutter was open
** optimal exposure - the maximum exposure* within dof and motion blur requirements without clipping important highlights.
*** under exposed - more exposure* could have been added with the DOF and blur constraints still being met without clipping important highlights.