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

Execution · Competitive PvP
Timing-based basketball execution layered over playbook knowledge and opponent prediction.

Execution · Competitive PvP
Tactical gunfights testing aim, entry planning and prediction of human opponents online.
NBA 2K9 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.
NBA 2K9
Shot timing and stick handles set the ceiling
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.
NBA 2K9
Online defenders bait passes and adapt to your sets
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.
NBA 2K9
Shot RNG and bounces add bounded 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.
NBA 2K9
Playbooks, matchups and roster management are learnable systems
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.