About the time the DAC technology had matured, it seemed like two things happened: (1) music compression for portable devices became popular (128 kbps - ugh!), and (2) music CDs were being remastered for a higher loudness level at a given volume setting.
The latter had the net effect of compressing the music and reducing the dynamic range as compared to the original mastering. Some collectors make an effort to locate the original masterings if they didn't already own them (or made the mistake of selling them when they bought the new "remasters").
That's true. The engineers have to understand the underlying capabilities to get the most out of it. There are other issues as well. Many sound engineers working on major labels and stuff are more likely to be in their 40s-50s, rather than being young whippersnappers, so they are going to be affected by hearing issues that inevitably come with age. That is going to effect the mix to a degree.