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

Execution · Practiced Mastery
Precision sniping and arena navigation through fixed, gimmick-laden levels.

Execution · Practiced Mastery
Mario's compact Game Boy debut with odd physics, shooter stages, and Sarasaland instead of the Mushroom Kingdom.
MDK leans Execution (Practiced Mastery); Super Mario Land leans Execution (Practiced Mastery).
Same score on execution - which means the number cannot separate them. The difference is in what each one asks of you.
MDK
Sniper-mode precision and arena dodging demand steady hands
Super Mario Land
Tiny screen and slippery physics demand careful jumps
Same score on reads - which means the number cannot separate them. The difference is in what each one asks of you.
MDK
Alien enemies behave on fixed scripts
Super Mario Land
Fully scripted patterns
Same score on variance - which means the number cannot separate them. The difference is in what each one asks of you.
MDK
Levels are authored with nothing random
Super Mario Land
Minor secret rooms, quickly mapped
Same score on optimization - which means the number cannot separate them. The difference is in what each one asks of you.
MDK
Learning arena gimmicks and item use solves each level
Super Mario Land
Short levels with simple optimal routes
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.