head to head
Neither is simply harder - they are hard in different places. Divekick demands more reads; Dragon Ball Z: Budokai 3 demands more execution.

Reads · Pure Mind Games
A two-button parody fighter that strips fighting games down to pure one-hit-kill spacing reads.

Execution · Competitive PvP
An anime fighter testing combo execution and counter-baiting against human opponents.
Divekick leans Reads (Pure Mind Games); Dragon Ball Z: Budokai 3 leans Execution (Competitive PvP).
Dragon Ball Z: Budokai 3 leans clearly harder on execution.
Divekick
Two buttons, one-hit kills; almost no physical ceiling.
Dragon Ball Z: Budokai 3
Combo execution, teleport counters and beam timing demand hands
Divekick leans clearly harder on reads.
Divekick
Pure spacing yomi against an adapting human is the entire game.
Dragon Ball Z: Budokai 3
Versus humans, baiting teleports and guessing cancels decides exchanges
Same score on variance - which means the number cannot separate them. The difference is in what each one asks of you.
Divekick
Fully deterministic.
Dragon Ball Z: Budokai 3
Almost nothing random beyond minor clash inputs
Dragon Ball Z: Budokai 3 leans a little harder on optimization, though the gap is small.
Divekick
Character angles and gem choices are quickly mapped.
Dragon Ball Z: Budokai 3
Capsule builds and matchup knowledge underpin competitive play
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.