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
A football sim where reading opponents and precise execution both decide matches.

Execution · Competitive PvP
Tactical gunfights testing aim, entry planning and prediction of human opponents online.
FIFA 20 leans Execution (Grand Arena); Tom Clancy's Rainbow Six: Vegas leans Execution (Competitive PvP).
Same score on execution - which means the number cannot separate them. The difference is in what each one asks of you.
FIFA 20
precise passing, dribbling, and shot timing
Tom Clancy's Rainbow Six: Vegas
Aim and snap-to-cover gunplay punish slow hands
FIFA 20 leans a little harder on reads, though the gap is small.
FIFA 20
reading human opponent tactics live
Tom Clancy's Rainbow Six: Vegas
Multiplayer angles and pushes demand reading human opponents
Same score on variance - which means the number cannot separate them. The difference is in what each one asks of you.
FIFA 20
minor ball physics and injury randomness
Tom Clancy's Rainbow Six: Vegas
Terrorist hunt spawns vary modestly between runs
FIFA 20 leans a little harder on optimization, though the gap is small.
FIFA 20
formations and player builds solvable
Tom Clancy's Rainbow Six: Vegas
Room-entry planning and map knowledge are studyable
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.