head to head
Neither is simply harder - they are hard in different places. StarCraft demands more optimization; War Thunder demands more variance.

Optimization · Grand Arena
A real-time strategy classic where perfected build orders and mechanical speed decide most matches.

Execution · Grand Arena
Sim-leaning combined-arms vehicle PvP.
StarCraft leans Optimization (Grand Arena); War Thunder leans Execution (Grand Arena).
Same score on execution - which means the number cannot separate them. The difference is in what each one asks of you.
StarCraft
APM and micro control ceiling is huge
War Thunder
Aim, lead, and vehicle handling demanding
Same score on reads - which means the number cannot separate them. The difference is in what each one asks of you.
StarCraft
scouting and predicting human opponent builds
War Thunder
Position-versus-position duels are reads
War Thunder leans clearly harder on variance.
StarCraft
minimal hidden info beyond fog of war
War Thunder
Shell ballistics and matchmaking vary
StarCraft leans clearly harder on optimization.
StarCraft
build orders and economy are near-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.