head to head
Neither is harder. They score identically on all four axes, so the difference between them is in kind, not degree.

Execution · Practiced Mastery
Arcade-style western shooter built around stage gunfights and showdown duels.

Execution · Practiced Mastery
Top-down aim and kiting against scripted alien swarms with light upgrade planning.
Red Dead Revolver leans Execution (Practiced Mastery); Shadowgrounds leans Execution (Practiced Mastery).
Same score on execution - which means the number cannot separate them. The difference is in what each one asks of you.
Red Dead Revolver
Arcade gunplay and duel timing dominate
Shadowgrounds
Kiting alien swarms top-down rewards steady aim and movement
Same score on reads - which means the number cannot separate them. The difference is in what each one asks of you.
Red Dead Revolver
Enemies are scripted shooting-gallery foes
Shadowgrounds
Aliens charge on simple scripts, never modelling you
Same score on variance - which means the number cannot separate them. The difference is in what each one asks of you.
Red Dead Revolver
Minor spawn variation
Shadowgrounds
Ambush triggers are scripted-but-unknown on first playthrough
Same score on optimization - which means the number cannot separate them. The difference is in what each one asks of you.
Red Dead Revolver
Level layouts and duel rhythms are learnable
Shadowgrounds
Weapon upgrade routing is a light solvable layer
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.