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
Isometric movement control while herding Flickies along memorised routes.
MDK leans Execution (Practiced Mastery); Sonic 3D Blast 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
Sonic 3D Blast
Isometric momentum control and Flicky herding need precise movement
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
Sonic 3D Blast
Robotnik bosses run fixed 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
Sonic 3D Blast
Flicky and badnik placements never change
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
Sonic 3D Blast
Routing each zone for Flickies and emeralds is learnable
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.