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

Execution · Grand Arena
Crossover fighting game where groove systems and footsies meet deep execution demands.

Execution · Grand Arena
A combo system built on constant Combo Breaker mind-games that create a unique adaptive read-off at every moment of a combo.
Capcom vs. SNK 2: Mark of the Millennium 2001 leans Execution (Grand Arena); Killer Instinct (2013) leans Execution (Grand Arena).
Same score on execution - which means the number cannot separate them. The difference is in what each one asks of you.
Capcom vs. SNK 2: Mark of the Millennium 2001
Strict links, roll cancels, groove mechanics
Killer Instinct (2013)
Shadow counters and Combo Breaker timing demand very precise inputs
Killer Instinct (2013) leans a little harder on reads, though the gap is small.
Capcom vs. SNK 2: Mark of the Millennium 2001
Footsies and conditioning against adapting humans
Killer Instinct (2013)
Combo Breaker prediction is a pure read-off against an adaptive opponent
Same score on variance - which means the number cannot separate them. The difference is in what each one asks of you.
Capcom vs. SNK 2: Mark of the Millennium 2001
Almost no randomness in matches
Killer Instinct (2013)
No RNG; all mechanics are fully visible
Killer Instinct (2013) leans a little harder on optimization, though the gap is small.
Capcom vs. SNK 2: Mark of the Millennium 2001
Groove selection, team order, matchup theory
Killer Instinct (2013)
Instinct activation timing and optimal opener routes are well-studied
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.