head to head
Neither is harder. They score identically on all four axes, so the difference between them is in kind, not degree.

Execution · Pure Mechanics
A fast military shooter where twitch aim against human opponents defines success.

Execution · Pure Mechanics
Classic arena aim married to champion abilities, tested against adaptive human opponents in fast duel maps.
Call of Duty: Black Ops 4 leans Execution (Pure Mechanics); Quake Champions leans Execution (Pure Mechanics).
Same score on execution - which means the number cannot separate them. The difference is in what each one asks of you.
Call of Duty: Black Ops 4
aim and reflexes decide most fights
Quake Champions
Champion abilities add execution layers on top of classic rail and rocket aim
Same score on reads - which means the number cannot separate them. The difference is in what each one asks of you.
Call of Duty: Black Ops 4
predicting human opponents' positioning
Quake Champions
Human duels require reading opponent ability usage and positioning
Same score on variance - which means the number cannot separate them. The difference is in what each one asks of you.
Call of Duty: Black Ops 4
battle royale loot is heavily random
Quake Champions
Ability cooldowns introduce mild timing uncertainty per match
Same score on optimization - which means the number cannot separate them. The difference is in what each one asks of you.
Call of Duty: Black Ops 4
loadouts and rotations are solvable
Quake Champions
Champion matchup knowledge and item timing are solvable advantages
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.