That's a very hard question to answer, as I don't know what exactly would have happened if he had been institutionalized. French psychiatrists has a very different approach than US ones (although that might change) when it comes to diagnosis, so it's really hard to say.

A question could be - what would have been the goals of institutionalizing him? To make him more fit for life in our society with our standards; or to prevent him from harming others and himself?

Since you're asking specifically if he would have been better off, I'm assuming the former of the two- in which case no, I don't think he'd have been better off. I do think he's physiologically incapable of sitting at a desk, taking orders, living in an extremely codified manner where one has to respect certain hierarchies, hide certain feelings, etc. - and that perhaps he has now found a way to detach himself from it. I don't think that any institution could have addressed that.

But I'm sure that there are some people (former teachers, classmates, etc.) who think it'd have been better if he had been institutionalized.