The new tier likely reflects the addition of ray tracing.
Asobo confirmed that the initial download is only 30 GB.
Comparison of the same location in Microsoft Flight Simulator 2020 (top) and 2024 (bottom).

All environment assets have been updated with increased detail and a more advanced terrain generation system.
Microsoft and Asobo have also detailed the new career mode.
After purchasing and passing enough exams, players can eventually run their own airlines and manage fleets.
Flying also incorporates a new preflight check system involving on-foot inspections, weather planning, and mission briefings.