I believe on either the steam developer pages or reviewer pages they haven't updated it past the 2010 theme to this day. I don't recall which it is but you're not wrong.
Compared to most sites yeah, but still nothing like it was. I have to scroll 5 full page lengths just to get to the top sellers. Or I hover over New and Noteworthy, wait a second for the drop down to fade in and then click top sellers, we just don't need an animation on it.
It's just lots of carousels now and big oversized buttons.
The worst was changing the best controller configuration UI when they retired Old Big Picture. The UX was absolutely perfect and paired with a steam controller you could make fairly complex configs easily. Now I am forced to use the old linux client on linux to keep the UI but cannot enjoy the new compatibility stuff like gamescope.