Man City didn't beat FFP. They muddied the waters on 1 particular point and had their penalty reduced on final appeal over a technicality after a 2 year fight.
They've followed all other FFP rules prior and since to make sure they don't end up in the same place again.
(Of course, they are probably doing other shady accounting in extreme secrecy to make sure they don't fall foul of FFP again).
I don't know anything about PSG to comment on them.