I don't know if I would call that art, if we're talking about the traditional Parisian accent that is linked here (a popular accent, mostly used by lower classes). Today it sounds rather uneducated, and although it is easier to understand than many other local French accents, it doesn't sound especially clearer than modern speech.
Although it might sound clearer to English speakers because it features more word-level stress while standard French doesn't really have it (but this has not been lost recently).
I studied French for many years in high-school and college. I've since forgotten much of it, but I was able to easily follow this "uneducated" accent. At times I found myself not even needing to read the subtitles. I had forgotten some of the meanings, but I could pick out the words and structure. Compare this to when I was learning French: most of the spoken material was in a more modern accent and was spoken much more quickly (as is de rigueur). I wonder if some of these older accents may be useful in teaching.
Similarly I've been learning Spanish the past few years, and the most comprehensible accents are those from Guatemala, Nicaragua, and Honduras--some of the poorest Spanish-speaking countries. I cannot for the life of me understand a heavy Mexican or Chilean accent, but I can easily follow Guatemalan. It's interesting from a socio-linguistic perspective if nothing else.
No. The sentences are more elaborate and pronunciation, while heavily emphased in comparison with modern casual french, doesn't suffer yet from "word eating". Links(?) between words are also clearer, less mumbled together.
Although it might sound clearer to English speakers because it features more word-level stress while standard French doesn't really have it (but this has not been lost recently).