Network redundancy (sometimes up to quadruple for some of the French electrical infrastructure) is indeed vulnerable to asymmetrical attack, if the attacker knows what secures what.

I can throw burning fuel into a manhole or at a street cabinet, and it doesn't take much insight to find one that carries important traffic - take your pick near a military base or a nuclear power plant. But the attack will be ineffective, because the attacker needs to know what other bits of infrastructure carry the backup circuits - and take them out simultaneously. And, of course, for the important stuff such information is classified. So, an effective attack on French critical infrastructure is more difficult than it seems at first glance.