I've also noticed on a clear day, it's too bright and the overcast is much too dark.
They appear to be trying to replicate the human iris by adjusting the light levels with brightness gain control acting on the interior and the exterior views. Similar to real life this depends on the ratio of your inside to outside view and I guess would be difficult to achieve a good balance.
I've always used TrackIR and have found that if I set the FS 2020 pilot view (in the C172 with steam gauges) to view outside plus only the first two rows of gauges then at midday with clear skies lower the outside view brightness, gamma etc to your liking with GeForce Experience so the inside panel is a little on the dark side. You'll find when you look down with TrackIR at the panel it will appear normal brightness, as in real life your eyes adjust to tthe inside lighting.
Then do exactly the same with heavy cloud cover. It's a fine balance and difficult but I've found a reasonably happy medium, not perfect but far better in my opinion than previousl settings.
This won't suit everyone, just my 10 cents worth.
It would be good if MS could find the right balance to keep everyone happy.