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
Gunplay and predicting human squads across large-scale and extraction modes.

Execution · Competitive PvP
Tactical gunfights testing aim, entry planning and prediction of human opponents online.
Delta Force leans Execution (Competitive PvP); Tom Clancy's Rainbow Six: Vegas leans Execution (Competitive PvP).
Delta Force leans a little harder on execution, though the gap is small.
Delta Force
Gunfights and recoil control decide most engagements
Tom Clancy's Rainbow Six: Vegas
Aim and snap-to-cover gunplay punish slow hands
Delta Force leans a little harder on reads, though the gap is small.
Delta Force
Predicting human rotations and pushes runs through every mode
Tom Clancy's Rainbow Six: Vegas
Multiplayer angles and pushes demand reading human opponents
Delta Force leans a little harder on variance, though the gap is small.
Delta Force
Extraction loot and operator gadget chaos add noise
Tom Clancy's Rainbow Six: Vegas
Terrorist hunt spawns vary modestly between runs
Same score on optimization - which means the number cannot separate them. The difference is in what each one asks of you.
Delta Force
Loadout economy and objective sequencing set the floor
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.