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
Lab-honed combo execution plus live mixup guessing against adapting human opponents.

Execution · Grand Arena
A tag-team crossover fighter pitting Street Fighter's cast against Tekken's under Capcom rules.
Skullgirls: 2nd Encore leans Execution (Competitive PvP); Street Fighter X Tekken leans Execution (Grand Arena).
Skullgirls: 2nd Encore leans a little harder on execution, though the gap is small.
Skullgirls: 2nd Encore
Long combo routes and tight conversions demand serious 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.
Skullgirls: 2nd Encore
Mixups and resets only work by out-guessing a human
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.
Skullgirls: 2nd Encore
Fully deterministic fighter 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.
Skullgirls: 2nd Encore
Team composition, assists and combo theory go 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.