I cross the Peripherique everyday and I believe some use Peripherique too much as a scapegoat when it's far from being the only culprit.
I think one of the main issue about the Peripherique is not the beltway itself but its nearest surroundings especially those inside Paris limits.
There is a several hundred meters large stretch around the Peripherique very badly urbanized where the City of Paris has the habit to put all low-value equipments or anything that take too much space. Cemetaries, parks, sports field, warehouses...
This is Porte d'Orleans
The left side of the Peripherique is the municipality of Montrouge and the right side is the City of Paris.
On Montrouge side, dense urbanity begins right after the Peripherique while on the City of Paris side, there is a gap of several hundred meters.
This gap creates a bigger barrier than the freeway in my opinion.
