The latest version of Littlenavmap uses Navigraph airspace view by default. fsAerodata includes a much richer detail including airspace airways, MATZ sectors, ARTCC sectors, and different ARTCC altitude layers. Please follow the next steps to enable it:
Go to Menu -> View -> Airspace Sources -> Select Simulator and deselect Navigraph
Comparison of ARTCC Airspaces details: fsAerodata is depicted on the left.
Thanks,