Capacitors and or other electronic parts alone make no sound and therefore have no inherent sound quality.
Its how you put all the parts together in the design that results in "sound quality".
Implementation is key, sure, but I guess the case could be made just as well that implications into sonics are inherent to the components themselves.
Experts in all fields tend to become better over time so no doubt in my mind there is more expertise in designing good gear out there today than ever before. That's called progress and is probably the biggest difference. Today's experts have the expertise of all those in the past to draw upon. They may still innovate but there is a better body of knowledge available for them to start with so the good ones will likely produce even better products. That's progress.....
Progress.. I see what you mean, but most of the progress made today and through the last decades appears to be working around how to keep costs at bay through mass production, convenience (i.e.: size, consumption, etc.) et al. and hereby lessening the impact of such factors. Oftentimes "developments" resemble a rewrite in disguise in the effort to wow and lure its costumers into ongoing purchases with the promise of better and better sonics. If one were to read all hifi magazines through the last 30-40 years and follow the development of how the reviewers reflected progressively positive on the coming iterations of, say, Mark Levinson amps, the current versions should almost sound as good as to cure severe illnesses as a side effect. It's symptomatic to much of the hifi industry at large: reveling so locally, and navel-gazingly, as to miss the bigger picture.
It's not that I don't see a progression into making amps sound better, but it seems the class-D segment is more or less the sole beneficiary without raising the bar in absolute terms, although getting closer to the best out there. That's definitely progression and exciting in many ways (also as to accommodate the environment, not least).