head to head
Neither is simply harder - they are hard in different places. Rocksmith 2014 demands more execution; Super Mario World demands more optimization.

Execution · Pure Mechanics
A pure physical-execution trainer - playing a real guitar accurately on time.

Execution · Pure Mechanics
Precise jump execution across fixed levels with secrets to memorise.
Rocksmith 2014 leans Execution (Pure Mechanics); Super Mario World leans Execution (Pure Mechanics).
Rocksmith 2014 leans clearly harder on execution.
Rocksmith 2014
Real fretting and picking accuracy is literally the whole game
Super Mario World
Perfect inputs trivialise every jump, spin and cape flight
Same score on reads - which means the number cannot separate them. The difference is in what each one asks of you.
Rocksmith 2014
No opponent, only the song
Super Mario World
Scripted Koopas adapt to nothing
Super Mario World leans a little harder on variance, though the gap is small.
Rocksmith 2014
Charts are fully known in advance
Super Mario World
Levels are fixed; nothing hidden survives one playthrough
Super Mario World leans clearly harder on optimization.
Rocksmith 2014
Practice scheduling helps but solves nothing for your hands
Super Mario World
Secret exits and route knowledge add a modest 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.