head to head
Neither is meaningfully harder - they pose close to the same test. The widest gap is execution, and it is a single point.

Execution · Grand Arena
Build-fight battle royale with deep mechanics.

Execution · Grand Arena
Sim-leaning combined-arms vehicle PvP.
Fortnite leans Execution (Grand Arena); War Thunder leans Execution (Grand Arena).
Fortnite leans a little harder on execution, though the gap is small.
Fortnite
Build-edit-aim combos punish slow hands
War Thunder
Aim, lead, and vehicle handling demanding
Fortnite leans a little harder on reads, though the gap is small.
Fortnite
Box fights are pure adaptive mind games
War Thunder
Position-versus-position duels are reads
Same score on variance - which means the number cannot separate them. The difference is in what each one asks of you.
Fortnite
Loot drops, storm, item rotations vary
War Thunder
Shell ballistics and matchmaking vary
War Thunder leans a little harder on optimization, though the gap is small.
Fortnite
Loadouts, mats economy, rotations solvable
War Thunder
Vehicle lineups and module unlocks deep
A matching score does not mean a matching test. Two games can both sit at 10 on execution and demand completely different things of you - which is why the reasoning above matters more than the number beside it.