head to head
Neither is simply harder - they are hard in different places. Red Dead Redemption 2 demands more variance; Sonic Generations demands more execution.

Execution · Practiced Mastery
A cinematic open-world western leaning on shooting feel and atmosphere.

Execution · Practiced Mastery
Executing memorised high-speed routes through deterministic platforming levels.
Red Dead Redemption 2 leans Execution (Practiced Mastery); Sonic Generations leans Execution (Practiced Mastery).
Sonic Generations leans clearly harder on execution.
Red Dead Redemption 2
Gunplay and Dead Eye reward aim and timing.
Sonic Generations
Holding speed through precise jumps and boosts is the test
Red Dead Redemption 2 leans a little harder on reads, though the gap is small.
Red Dead Redemption 2
Enemies use scripted AI patterns, not adaptation.
Sonic Generations
No opponent; bosses are fixed patterns
Red Dead Redemption 2 leans clearly harder on variance.
Red Dead Redemption 2
Some hunting and weather randomness, lightly hidden.
Sonic Generations
Levels are fully deterministic
Sonic Generations leans clearly harder on optimization.
Red Dead Redemption 2
Loadouts and routes solvable but loose.
Sonic Generations
S-ranks come from memorising optimal routes and shortcuts
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.