Real Madrid may not need Mbappe at all either. I'm also not sure if Madrid would get much better then, because won't Benzema become a kind of 2nd striker if you let Mbappe play for Madrid too? I think Benzema will be much less in his role then. The most efficient striker is currently at Barcelona. Now that it's there, the title fight can get pretty exciting. Barcelona only has some problems to solve defensively in the back. In that respect, Real Madrid is better, but as said, Barcelona should especially lose points against the low-ranked teams.
That's maybe, commonly there will be only one superstar in a club. But if Mbappe is exactly in Real Madrid, at least they may be able to work and play together. But let it be, Mbappe is not in Real Madrid.
Barcelona only needs time for all players to be common playing in that club entirely. They will adapt as much as possible later. Probably, this is only the starting point, and some players may be still in the new mode and club solidity, so it may not be easy enough to adapt to the new club, moreover with new strategy and game mode.