I would caution against extrapolating from your experience. You must have been living in a good district with a decent school (and if you've been in France for any period of time you'll know that fighting for the right school is almost the most important thing in parents' lives and can even decide elections). Crucially, as there are much fewer private schools in France than say the UK or the US, the elite will instead make public superschools and then use connections and districts to put their kids in them (and get the taxpayer to foot the bill), the most famous being Henri IV and Louis le Grand in Paris, but this system applies to all regions (AFAIK).

Anecdotal evidence: my "college" or middle school equivalent (which I won't name and shame) in Grenoble had a much less interesting canteen. For example, the fries (served with every meal) were undercooked, sometimes still frozen inside, and we occasionally found worms. The queue for food could be as long as 45 minutes, forcing everybody to gulp down their food as fast as they could so as not to be late to the next class. The food was always deep fried meat or equivalents. A decent part of the student population was quite fat, although not to US or UK levels of obesity.

France is like the US. You have areas like Manhattan or Santa Monica, and you have areas like North Virginia or Ohio, all with their own history, local funding, civil servants providing wildly differing levels of service. Paris is almost another country (and its residents definitely see "provinciaux" as foreigners), maybe even more so than with London and the UK.

For a deep dive down the other end, I recommend the movie "Journee de la Jupe" which gives you a taste of the ZEP schools (arguably the worst in France), it's a bit more realistic than "Banlieue 13".