head to head
Neither is simply harder - they are hard in different places. Agar.io demands more execution; Among Us 3D demands more reads.

Reads · Competitive PvP
A browser arena where your cell eats smaller players and flees bigger ones.

Reads · Pure Mind Games
A first-person social deduction game about deceiving and reading human players.
Agar.io leans Reads (Competitive PvP); Among Us 3D leans Reads (Pure Mind Games).
Agar.io leans clearly harder on execution.
Agar.io
Mouse steering and split timing
Among Us 3D
Movement and tasks need no real motor skill
Among Us 3D leans clearly harder on reads.
Agar.io
Baiting and predicting human blobs decides fights
Among Us 3D
Deceiving and reading human players is the entire game
Among Us 3D leans a little harder on variance, though the gap is small.
Agar.io
Spawn locations and lobby makeup random
Among Us 3D
Impostor assignment and alibis are hidden information
Same score on optimization - which means the number cannot separate them. The difference is in what each one asks of you.
Agar.io
Split-merge math is shallow but real
Among Us 3D
Task efficiency and meeting logic are light systems
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.