does he have a functioning system around him at barca?
No, but you can argue a large part of why the system is so broken is because every manager that inherits Leo has to build a team around him that accounts for all the imbalances his play style burdens us with.
KDB can fit into any system as an "8" and will succeed. Lewa can be plugged into any system as a "9" and will be world class. These players can be key players of very successful teams without the coach having to bend the system very much to accommodate their every whim.
Let's say Leo goes to City next season. What is his position? How does Pep find two other attackers that fit with him? How do you cover for the space he does not defend? How do you make up for the lack of width on the right? How do you construct a proper passing system without Leo moving off the ball very much? How do you approach counters? etc.
These sorts of questions do not apply to De Bruyne or Lewandowski. You plug them into you lineup and they will execute their roles to perfection.