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

Reads · Competitive PvP
A 3D arena fighter where extendable-arm punches curve mid-flight in PvP duels.

Reads · Pure Mind Games
A two-button parody fighter that strips fighting games down to pure one-hit-kill spacing reads.
ARMS leans Reads (Competitive PvP); Divekick leans Reads (Pure Mind Games).
ARMS leans clearly harder on execution.
ARMS
Curving punches and dodge timing
Divekick
Two buttons, one-hit kills; almost no physical ceiling.
Divekick leans clearly harder on reads.
ARMS
Whiff-punish games against adapting humans
Divekick
Pure spacing yomi against an adapting human is the entire game.
ARMS leans a little harder on variance, though the gap is small.
ARMS
Minor stage and item randomness
Divekick
Fully deterministic.
ARMS leans a little harder on optimization, though the gap is small.
ARMS
Arm loadout counters and matchup study
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.