I think the pack size is actually 1:1 with Legacy client, just my impression. As for brightness, we're stuck with it; using the brightness slider only affects the game window. The only immediate way around it is to adjust your monitor.
The containers are really dark, though, as are some graphics. Coloured tribal masks look nearly identical (even the brightest ones), containers such as blackrock or bloodwood are almost completely lost in the main pack.
Maybe there's some way to manually access the game's gamma settings, or perhaps there's a Command for it.