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

Execution · Competitive PvP
Mobile shooter execution with human prediction, plus loot variance in battle royale.

Execution · Competitive PvP
Tactical gunfights testing aim, entry planning and prediction of human opponents online.
Call of Duty: Mobile leans Execution (Competitive PvP); 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.
Call of Duty: Mobile
Touch or controller aim and movement decide gunfights
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.
Call of Duty: Mobile
Human lobbies adapt rotations and peeks each match
Tom Clancy's Rainbow Six: Vegas
Multiplayer angles and pushes demand reading human opponents
Call of Duty: Mobile leans a little harder on variance, though the gap is small.
Call of Duty: Mobile
Battle royale drops and loot add run-to-run randomness
Tom Clancy's Rainbow Six: Vegas
Terrorist hunt spawns vary modestly between runs
Tom Clancy's Rainbow Six: Vegas leans a little harder on optimization, though the gap is small.
Call of Duty: Mobile
Loadout meta and map spawn knowledge reward study
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.