Go to a graduation ceremony at a top school (note: it's delayed 1-2 years after graduation) and you'll learn that the top 10% have ALL left the country, no exception.

(I'm talking about the top in terms of technical abilities, entrepreneurship and/or skills that are valuable to execute , not necessarily school grades).

Many of these students do start their careers elsewhere, partly due to the way the curriculum is planned (which leads many of them to finish their studies abroad). If you do look for them for your company/startup you'll be able to see them, although you could have to dig a bit deeper due to the small size of these programs (advertising in one specific French university does not have the same impact as in the UK/US and most other countries in the world).

Surprising because if a first world nation with high quality life in so many ways faces this problem what about the rest of the world.

Moved for the job. Stayed abroad for the job and the money.

Then whenever you look at what the country has to offer if you ever go back, you're like: "Fuckkkkkkkk" (yeah, it's that much of a disaster).

But i am in an engineering school, i am in the top 10%, and it is true.

There was even a note from the ministry this year asking engineering school to stop the mandatory semester in a foreign university for all engineering student, to try to reduce the drain.

There are some schools which are relatively young and focus on coding. Historically they were expensive (for French schools), even though one of them is now free thanks to the generosity of a French billionaire. They recruit students with different profiles than the traditional "Grandes Écoles" and they get much less recognition from French employers, especially large companies. Because of that, their top students may indeed be inclined to move abroad, where degrees matter less.

In the more generalist, traditional engineering Grandes Écoles, however, the phenomenon is a lot less prevalent. Some students do move abroad, but my experience is that it is not correlated to their competence. Those with propensity to found companies are more likely to go to the US, but that is mostly because the ecosystem there is like no other. On the other hand, you may have noticed that some large US companies (Google, Facebook...) have been opening research labs in Paris, while top French companies such as Criteo send their marketing department to the US but keep development in France. This is not only because talent is cheaper (others have already explained how low salaries for not mean low costs) but also because top technical talent doesn't necessarily want to emigrate. This is cliché, but Fabrice Bellard is still living in France, and Yann Le Cun moved back. :)

I am dubious because as mentioned by hiq above, you would need to wait much more than 2 years to figure out who are the "best". Another reason I am dubious is that working in France or at least in a French company is still the best way to climb the hierarchy fast when you're coming from X/Central Paris/ Mines de Paris/Telecom/etc... except for a few specific fields (finance comes to mind).

For those in those French "Ivy league" it makes sense to stay in a non-meritocracy / credentials based company then, but for all other engineering schools, it's a better deal to get a 6 figures salary job in the US, where it's much closer to a meritocracy than in traditional French companies.

In US tech you certainly see some Harvard, Stanford, mit graduates, but also a lot of non ivy league colleges with jobs such as software engineer, program manager, management, etc. One extreme example is Satya Nadella who got his MS from University of Wisconsin. Even if is undergrad degree was prestigious is India, it doesn't have the ivy League "power" similar to a X/Centrale/Mines in France or Harvard in the US in traditional jobs.

However, if you're from these schools but have nothing except your hard work to sell, you're better off in UK/USA (and your alumni network definitely extends there)... but you're likely a Parisian with friends/family/housing in Paris, so there are strong incentives to stay in the place you already are. Your school name alone will afford you a career decent enough for little effort.

For someone from any other school who ain't Parisian, there is no incentive to emigrate to Paris. The opportunities are much better in the UK/USA to the point of insanity, and it may even be easier logistically (it was for me).

For an European. Why the hell would he go to Paris? It's not even worth if for French people who ain't already in Paris.

How much does the dynamic part of the French society offered you for you work?