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
Weapon-based dueling testing spacing execution and mixup prediction against humans.

Execution · Grand Arena
A tag-team crossover fighter pitting Street Fighter's cast against Tekken's under Capcom rules.
SoulCalibur III leans Execution (Competitive PvP); Street Fighter X Tekken leans Execution (Grand Arena).
Street Fighter X Tekken leans a little harder on execution, though the gap is small.
SoulCalibur III
Spacing, movement and just-frame timing demand real hands
Street Fighter X Tekken
Tag combos and juggle timing demand practiced hands
Same score on reads - which means the number cannot separate them. The difference is in what each one asks of you.
SoulCalibur III
Versus humans, conditioning and throw-mixup guessing decides rounds
Street Fighter X Tekken
Human mixups and tag baits require adaptation
Same score on variance - which means the number cannot separate them. The difference is in what each one asks of you.
SoulCalibur III
Deterministic combat with nothing hidden
Street Fighter X Tekken
Deterministic aside from negligible elements
Street Fighter X Tekken leans a little harder on optimization, though the gap is small.
SoulCalibur III
Frame data, matchup study and stage knowledge run deep
Street Fighter X Tekken
Gem loadouts and team synergy add a builder layer
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.