To be clear, I wasn't professing to be an expert.

I'd hesitate to assume that French intelligence operatives have thoroughly penetrated terrorist groups and their sympathizers. My experience suggests that French authorities have for years underestimated the threat posed by such groups and are also significantly underfunded/under resourced.

The military patrol is primarily a form of security theatre, though that does depend upon the location. Some areas truly do need greater protection, such as repeatedly targeted venues, and those populations do need reassurance that they are not completely vulnerable. I also want to make clear that those forces can actually intervene in the unlikely situation that the protected venue is attacked, but it's also likely that their presence displaces the attacks to alternative sites.

Anyway, France has a significant population that is sympathetic to jihadi terrorism's goals and practices, and my understanding is that counterterrorism and terrorism response operations in France - both strategically and tactically - leave much to be desired. France/Paris is not like Munich circa 1972 (shit-show level of unpreparedness), but there's significant room for improvement.