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

Execution · Practiced Mastery
Arena duels mixing twitch dodge-punish play with RPG build preparation.

Execution · Competitive PvP
Tactical gunfights testing aim, entry planning and prediction of human opponents online.
Dissidia Final Fantasy leans Execution (Practiced Mastery); 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.
Dissidia Final Fantasy
Aerial dashes, dodge timing and punishes demand fast hands
Tom Clancy's Rainbow Six: Vegas
Aim and snap-to-cover gunplay punish slow hands
Same score on reads - which means the number cannot separate them. The difference is in what each one asks of you.
Dissidia Final Fantasy
Human duels hinge on baiting bravery attacks and dodges
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.
Dissidia Final Fantasy
Some equipment and summon randomness, mostly known state
Tom Clancy's Rainbow Six: Vegas
Terrorist hunt spawns vary modestly between runs
Dissidia Final Fantasy leans a little harder on optimization, though the gap is small.
Dissidia Final Fantasy
Builds, accessories and matchup knowledge shape every duel
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.