head to head
Agar.io asks more than Naruto Shippuden: Ultimate Ninja Storm 2, and the gap is reads.

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

Execution · Competitive PvP
Substitution baiting against humans atop simple anime-fighter inputs and team picks.
Agar.io leans Reads (Competitive PvP); Naruto Shippuden: Ultimate Ninja Storm 2 leans Execution (Competitive PvP).
Naruto Shippuden: Ultimate Ninja Storm 2 leans a little harder on execution, though the gap is small.
Agar.io
Mouse steering and split timing
Naruto Shippuden: Ultimate Ninja Storm 2
Timing substitutions and combos matters but inputs are simple
Agar.io leans clearly harder on reads.
Agar.io
Baiting and predicting human blobs decides fights
Naruto Shippuden: Ultimate Ninja Storm 2
Versus humans, baiting substitutions is the real layer
Agar.io leans clearly harder on variance.
Agar.io
Spawn locations and lobby makeup random
Naruto Shippuden: Ultimate Ninja Storm 2
Nothing hidden once both characters are known
Naruto Shippuden: Ultimate Ninja Storm 2 leans a little harder on optimization, though the gap is small.
Agar.io
Split-merge math is shallow but real
Naruto Shippuden: Ultimate Ninja Storm 2
Team composition and chakra management have solvable lines
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.