Strong disagree. Borderless icons floating in a sea of flatness is not "more sophisticated" by any means than the fully-customisable UI which was common in the XP era, and the huge amount of "skinning" that was also very popular. Transparent/translucent effects became common with Vista and that was run on the GPU, which was in general much less powerful than the ones today.
I'll add a 5th point: Thanks to a low barrier to entry, the average developer now is much lower quality than the average 20 years ago.