head to head
Neither is meaningfully harder - they pose close to the same test. The widest gap is reads, and it is a single point.

Execution · Practiced Mastery
Lightgun quick-draw reflexes against memorisable filmed ambush sequences.

Execution · Pure Mechanics
An arcade test of jump timing and enemy-flipping precision on a single screen.
Mad Dog McCree leans Execution (Practiced Mastery); Mario Bros. leans Execution (Pure Mechanics).
Same score on execution - which means the number cannot separate them. The difference is in what each one asks of you.
Mad Dog McCree
Quick-draw lightgun accuracy under strict timers
Mario Bros.
Precise jumps and bump timing under crowding enemies decide survival
Mario Bros. leans a little harder on reads, though the gap is small.
Mad Dog McCree
Outlaws appear in filmed, fixed sequences
Mario Bros.
Versus mode adds light human interference, enemies are scripted
Same score on variance - which means the number cannot separate them. The difference is in what each one asks of you.
Mad Dog McCree
Some ambush order shuffling, quickly mapped
Mario Bros.
Enemy spawns vary slightly but patterns are quickly learned
Mad Dog McCree leans a little harder on optimization, though the gap is small.
Mad Dog McCree
Memorising who pops out where is the real progression
Mario Bros.
POW block usage and enemy routing have known best lines
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.