I'd say it is unique that we obsess about players from Arsenal and PSG. We dont see this type of strategy in other top clubs IMO. They go for younger players from leagues like Ligue 1, Dutch top division, Portugese league etc. Perhaps because they have a more extensive scout network, I dont know.
When you say Barca are obsessed with PSG and Arsenal players you make it sound worse than it is. From Arsenal, only Farbregas was pursued heavily, and the Masia roots explain why. Song was a dumb signing regardless of Arsenal or not. As for PSG, it's only been the foolish pursuit of Marquinhos and TS, and with good reason I might add, both are really good.
You want Barca to buy young players from inferior league, but that is not how Barca operate. Firstly, Barcelona has had La Masia churning good talent for a few years to suplement the young player pool, so they've had less of a need to buy those project players elsewhere. Secondly the team is competing every single year for every single trophy available, you don't do that with 20 year old from Ligue 1, Eredivisie, or Primeira Liga. Like I said, those are type of players you buy as projects, not as main players. You need established world class talent to compete.
Also, barca buy young players from La Liga instead. Rakitic, Alba, Alves. all from La Liga.