head to head
Neither is simply harder - they are hard in different places. Grand Theft Auto: San Andreas demands more optimization; Transformers: Fall of Cybertron demands more execution.

Optimization · Practiced Mastery
A sprawling open-world crime epic with RPG-style character stats across a whole state.

Execution · Practiced Mastery
Cinematic third-person shooter campaign of set-piece battles across a dying Cybertron.
Grand Theft Auto: San Andreas leans Optimization (Practiced Mastery); Transformers: Fall of Cybertron leans Execution (Practiced Mastery).
Transformers: Fall of Cybertron leans clearly harder on execution.
Grand Theft Auto: San Andreas
Flying school and drive-bys need decent hands
Transformers: Fall of Cybertron
Third-person gunplay and transform-dodging carry combat
Transformers: Fall of Cybertron leans clearly harder on reads.
Grand Theft Auto: San Andreas
Gang AI is scripted, never adaptive
Transformers: Fall of Cybertron
Multiplayer modes add some human opposition
Same score on variance - which means the number cannot separate them. The difference is in what each one asks of you.
Grand Theft Auto: San Andreas
Territory wars and traffic add light randomness
Transformers: Fall of Cybertron
Scripted campaign with minor drop randomness
Grand Theft Auto: San Andreas leans clearly harder on optimization.
Grand Theft Auto: San Andreas
Stats, gym, weapon skill, and routes reward systematic play
Transformers: Fall of Cybertron
Weapon upgrades and loadouts reward light planning
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.