head to head
Neither is simply harder - they are hard in different places. Super Mario World demands more optimization; WarioWare, Inc.: Mega Microgame$! demands more variance.

Execution · Pure Mechanics
Precise jump execution across fixed levels with secrets to memorise.

Execution · Pure Mechanics
Rapid-fire recognition and reaction across hundreds of five-second microgames.
Super Mario World leans Execution (Pure Mechanics); WarioWare, Inc.: Mega Microgame$! leans Execution (Pure Mechanics).
WarioWare, Inc.: Mega Microgame$! leans a little harder on execution, though the gap is small.
Super Mario World
Perfect inputs trivialise every jump, spin and cape flight
WarioWare, Inc.: Mega Microgame$!
Reacting correctly in five-second microgames is the entire challenge
Same score on reads - which means the number cannot separate them. The difference is in what each one asks of you.
Super Mario World
Scripted Koopas adapt to nothing
WarioWare, Inc.: Mega Microgame$!
No adaptive opponent - microgames are scripted
WarioWare, Inc.: Mega Microgame$! leans clearly harder on variance.
Super Mario World
Levels are fixed; nothing hidden survives one playthrough
WarioWare, Inc.: Mega Microgame$!
Random microgame order forces instant recognition each round
Super Mario World leans clearly harder on optimization.
Super Mario World
Secret exits and route knowledge add a modest solvable layer
WarioWare, Inc.: Mega Microgame$!
Each microgame's solution is trivial once seen
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.