head to head
Neither is simply harder - they are hard in different places. Rainbow Six Siege demands more reads; War Thunder demands more variance.

Reads · Grand Arena
A tactical breach-and-defend shooter driven by mind games over angles and gadgets.

Execution · Grand Arena
Sim-leaning combined-arms vehicle PvP.
Rainbow Six Siege leans Reads (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.
Rainbow Six Siege
Crisp aim required but TTK is unforgiving.
War Thunder
Aim, lead, and vehicle handling demanding
Rainbow Six Siege leans clearly harder on reads.
Rainbow Six Siege
Defenders adapt holds; attackers fake and bait.
War Thunder
Position-versus-position duels are reads
War Thunder leans clearly harder on variance.
Rainbow Six Siege
Site rotations only; loadouts deterministic.
War Thunder
Shell ballistics and matchmaking vary
War Thunder leans a little harder on optimization, though the gap is small.
Rainbow Six Siege
Operator picks, gadget placement, and utility usage.
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.