On any given screen there are strips of metal/plastic/tape along the edges of the screen which sort of "sculpt" the light, and focus it evenly onto the screen. I've seen cases in which these framing elements of the screen were loose, crooked, missing, etc., and this caused the lighting to become uneven. In other words, if the frame of the screen is warped, the light can sort of "leak out" of the screen and appear uneven, and I suspect some of your screen elements have been warped by liquid to the point where this is happening. Sometimes you can tape over the "leaks" and focus the light back on the screen, but with the severity in your situation, I'd say you most likely just need a new screen unit, although while taking it apart it would be interesting to see if you are able to manipulate the problem at all by applying pressure, using tape, etc. And of course I am talking about the inner screen unit and its frame, not the outer glass or bezel that is visible without taking the computer apart.
No, I don't think the inverter cable is the issue here. The inverter and cable are doing their job and getting light to the screen; the problem is with how the now-defective screen is distributing the light.