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 fourth Soulcalibur adds armor-breaking Soul Gauge pressure and Critical Finishes to its weapon dueling.

Execution · Competitive PvP
The classic 'dream match' team fighter widely held as KOF's most balanced competitive entry.
Soulcalibur IV 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.
Soulcalibur IV
Step-guard and just-guard timing keep a real physical ceiling.
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.
Soulcalibur IV
Critical Finish threats add layers to adaptive mixup guessing.
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.
Soulcalibur IV
Soul Gauge is visible; no hidden info.
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.
Soulcalibur IV
Guard-crush pressure routes and frame data are studyable.
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.