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

Execution · Pure Mechanics
The Guitar Hero entry that added drums and vocals to chase full-band play.

Execution · Pure Mechanics
A rhythm action retrospective replaying the Kingdom Hearts saga through its soundtrack.
Guitar Hero: World Tour leans Execution (Pure Mechanics); Kingdom Hearts: Melody of Memory leans Execution (Pure Mechanics).
Guitar Hero: World Tour leans a little harder on execution, though the gap is small.
Guitar Hero: World Tour
Fret-and-strum accuracy on expert note charts
Kingdom Hearts: Melody of Memory
Proud-mode charts mix attacks, jumps, and glides quickly
Same score on reads - which means the number cannot separate them. The difference is in what each one asks of you.
Guitar Hero: World Tour
Charts never adapt
Kingdom Hearts: Melody of Memory
Enemy waves are chart-scripted
Kingdom Hearts: Melody of Memory leans a little harder on variance, though the gap is small.
Guitar Hero: World Tour
Deterministic charts
Kingdom Hearts: Melody of Memory
Minor item drop randomness
Same score on optimization - which means the number cannot separate them. The difference is in what each one asks of you.
Guitar Hero: World Tour
Star power activation paths drive top scores
Kingdom Hearts: Melody of Memory
Team choice and chart memorization
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.