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

Execution · Competitive PvP
The Deadly Alliance follow-up adding combo breakers, death traps, and online play.

Execution · Competitive PvP
Weapon-based dueling testing spacing execution and mixup prediction against humans.
Mortal Kombat: Deception leans Execution (Competitive PvP); SoulCalibur III leans Execution (Competitive PvP).
Same score on execution - which means the number cannot separate them. The difference is in what each one asks of you.
Mortal Kombat: Deception
Style strings plus stage-hazard spacing demand control
SoulCalibur III
Spacing, movement and just-frame timing demand real hands
Same score on reads - which means the number cannot separate them. The difference is in what each one asks of you.
Mortal Kombat: Deception
Human opponents bait death traps and breakers
SoulCalibur III
Versus humans, conditioning and throw-mixup guessing decides rounds
Same score on variance - which means the number cannot separate them. The difference is in what each one asks of you.
Mortal Kombat: Deception
Deterministic outside known stage hazards
SoulCalibur III
Deterministic combat with nothing hidden
Same score on optimization - which means the number cannot separate them. The difference is in what each one asks of you.
Mortal Kombat: Deception
Combo routes and hazard positioning are lab work
SoulCalibur III
Frame data, matchup study and stage knowledge run deep
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.