if you never used the heater/defrost and they discolored, then that agrees with the assessment that disconnecting the defrost heater is not the solution

 

I find it very useful for about a week, twice a year. That's the stretch in the spring and in the fall where the is sun directly behind me, just above the horizon, during a stretch of my morning commute. During those weeks I very much enjoy the auto-dimming feature. The rest of the time I can't say as I really notice it either way