Profile Prism isn't doing it backwards; you are!  We are not blindly adding brightness to see if we can make an improvement.  We are adjusting the screen image so that it matches your print.  From the Profile Prism help under the topic of editing printer profiles:

"Use the controls on the editor window to make the right sample image (labeled "Print") at the top of the editor window look as close as possible to your print. Refer to the instructions below on how to accomplish this task, but remember that we are not doing any "correcting" on screen; just the opposite! We are making adjustments to make the right (print) image in the editor window look like the print. If the gray scale or gray areas in the print have a green cast, we need to make the right (print) image have the same green cast in those same gray areas in the image."

As far as soft proofs, that's about as good as soft proofs get.  They are hit or miss and should never be used to judge final prints.  There are too many compromises being made due to the fact that you have to have an accurate screeen profile, accurate printer profile, you have to be judging colors that are not out of gamut on either the screen or the printer, paper white is often far off from screen white, and many other issues.

Regards,
Mike