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

Execution · Pure Mechanics
Finger speed and accuracy against fixed note charts of 80s tracks.

Execution · Pure Mechanics
Cute two-button rhythm game where everything reduces to hitting notes on beat.
Guitar Hero Encore: Rocks the 80s leans Execution (Pure Mechanics); Muse Dash 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.
Guitar Hero Encore: Rocks the 80s
Hitting note charts at speed is a pure motor ceiling
Muse Dash
Two-lane rhythm hits at high BPM are pure hands
Same score on reads - which means the number cannot separate them. The difference is in what each one asks of you.
Guitar Hero Encore: Rocks the 80s
No opponent, just the chart
Muse Dash
Charts never adapt
Same score on variance - which means the number cannot separate them. The difference is in what each one asks of you.
Guitar Hero Encore: Rocks the 80s
Charts are fixed and fully memorisable
Muse Dash
Fully deterministic note charts
Same score on optimization - which means the number cannot separate them. The difference is in what each one asks of you.
Guitar Hero Encore: Rocks the 80s
Star power pathing squeezes out extra score
Muse Dash
Character buffs and chart memorization help margins
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.