I guess it goes back to the conference of reference tracks for me. If I worked on a mix where I really like how the bass turned out (using my ears exclusively), and I know for that mix that the bass was ~3db lower than the lead vocals, then the tools I'm talking about would help me apply the same bass/vocal relationship to a mix currently being worked.
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So you guys honestly wouldn't find a before/after curve interesting, I must just be a visual kind of guy.
If you insist on trying to do things by sight instead of using your ears, frankly, you're in the wrong hobby/vocation. Take up photography, where your painting of the Grannysmith apple on top of the yellow fire truck in the pool of green Vulcan blood will obviously have problems without you're even needing to pull up the histogram of the picture to show that it's all red when it's not supposed to be

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I don't mean to sound harsh, but frankly, you have no argument here; it holds no water, for several reasons.
First, if one track is 3dB louder (which is really a statement that means nothing on it's own unless you specify whether you're talking about RMS levels or peak levels or something else) than another in one song does not mean anything at all when it comes to what it should be in another song. You might as well say that every person on the planet should have such-and-such an eyeglass prescription because that's the prescription that this person wears.
Second, even if you do find a song where in can be argued that two tracks should be mixed relatively the same way as some reference track, there's no way that you'll be able to see and/or match that by looking at their FFTs in a spectrum analyzer. It just doesn't work that way. It just doesn't. Trust us.
Third, if you can't tell by listening whether the relative volume between two tracks sounds "right" to you or not, then there's no reason to even be doing this stuff. It would be like taking photographs for a hobby and not having any idea whether you even like the way they look or not.
Nothing personal, dude; you're not the first newb who's thought that all you need are enough of the right kind of plugs along with enough visual aids, and the computer will practically mix the music for you, and you won't be the last. But honestly and respectfully, the sooner you learn the hard fact that it is just plain impossible for it to work that way, the better off you'll be
G.