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

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

Reads · Pure Mind Games
A two-button parody fighter that strips fighting games down to pure one-hit-kill spacing reads.
Agar.io leans Reads (Competitive PvP); Divekick leans Reads (Pure Mind Games).
Agar.io leans clearly harder on execution.
Agar.io
Mouse steering and split timing
Divekick
Two buttons, one-hit kills; almost no physical ceiling.
Divekick leans clearly harder on reads.
Agar.io
Baiting and predicting human blobs decides fights
Divekick
Pure spacing yomi against an adapting human is the entire game.
Agar.io leans clearly harder on variance.
Agar.io
Spawn locations and lobby makeup random
Divekick
Fully deterministic.
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
Divekick
Character angles and gem choices are quickly mapped.
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.