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

Execution · Pure Mechanics
A rhythm game testing pure input timing on fixed DJ-flavored charts.

Execution · Pure Mechanics
Sequel rhythm game with harder setlists and refined plastic-guitar technique.
D4DJ Groovy Mix leans Execution (Pure Mechanics); Guitar Hero II 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.
D4DJ Groovy Mix
Note timing under disc-scratch mechanics is the entire test
Guitar Hero II
Harder charts, hammer-ons, and three-note chords
Same score on reads - which means the number cannot separate them. The difference is in what each one asks of you.
D4DJ Groovy Mix
No opponent - the chart never adapts
Guitar Hero II
Static note highways
D4DJ Groovy Mix leans a little harder on variance, though the gap is small.
D4DJ Groovy Mix
Charts are fixed; only event banners rotate
Guitar Hero II
Fully deterministic charts
D4DJ Groovy Mix leans a little harder on optimization, though the gap is small.
D4DJ Groovy Mix
Card scoring teams matter for events, not for skill
Guitar Hero II
Star power pathing for leaderboard play
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.