head to head
Neither is simply harder - they are hard in different places. Counter-Strike 2 demands more execution; Rainbow Six Siege demands more reads.

Execution · Competitive PvP
A round-based tactical shooter decided by aim duels and adapting to humans.

Reads · Grand Arena
A tactical breach-and-defend shooter driven by mind games over angles and gadgets.
Counter-Strike 2 leans Execution (Competitive PvP); Rainbow Six Siege leans Reads (Grand Arena).
Counter-Strike 2 leans clearly harder on execution.
Counter-Strike 2
Aim, spray control, and movement are the headline skills.
Rainbow Six Siege
Crisp aim required but TTK is unforgiving.
Rainbow Six Siege leans clearly harder on reads.
Counter-Strike 2
Five humans constantly adapting peeks, fakes, and timings.
Rainbow Six Siege
Defenders adapt holds; attackers fake and bait.
Counter-Strike 2 leans a little harder on variance, though the gap is small.
Counter-Strike 2
Spray RNG and unknown opponent positions add fog.
Rainbow Six Siege
Site rotations only; loadouts deterministic.
Rainbow Six Siege leans a little harder on optimization, though the gap is small.
Counter-Strike 2
Economy, util usage, and map theory are studyable.
Rainbow Six Siege
Operator picks, gadget placement, and utility usage.
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.