Remember, in real life, taking a picture, a lens would be on the camera, and wide open. There would be no visible or significant effect on the exposure in that case; the light coming in through the lens totally dominates, and that coming through the top LCD becomes insignificant.
You are wrong. We are seeing the change from sunlight to shadow change the exposure by as much as 1/2 stop when the shooter moves from daylight to shadow in real shooting conditions. I can confirm this with a bright sunlit beach photo shoot yesterday.
I tried that just now, no change in exposure from bright sun to shade as long as my viewfinder was covered. Uncover the viewfinder, or hold it to your eye so even a little light leaks by, and there is a large change from very bright sun to shade (when focused on the same subject.)
Were you shooting in your tests with the viewfinder blocked so there was no influence from light leaking in thru the viewfinder??