head to head
Neither is meaningfully harder - they pose close to the same test. The widest gap is execution, and it is a single point.

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

Execution · Competitive PvP
The classic 'dream match' team fighter widely held as KOF's most balanced competitive entry.
Mortal Kombat: Deception leans Execution (Competitive PvP); The King of Fighters '98 leans Execution (Competitive PvP).
The King of Fighters '98 leans a little harder on execution, though the gap is small.
Mortal Kombat: Deception
Style strings plus stage-hazard spacing demand control
The King of Fighters '98
Strict inputs, short hops, tight punishes
The King of Fighters '98 leans a little harder on reads, though the gap is small.
Mortal Kombat: Deception
Human opponents bait death traps and breakers
The King of Fighters '98
Human opponents constantly adapt and condition you
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
The King of Fighters '98
Near-fully visible game state
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
The King of Fighters '98
Team order and matchup theory reward study
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.