head to head
vs
Sid Meier's Pirates!vsSiren
Sid Meier's Pirates! leans Optimization (Pure Optimization); Siren leans Optimization (Pure Optimization).
Sid Meier's Pirates!Siren
Axis by axis
Execution4 vs 3
Sid Meier's Pirates! leans harder on execution: Sword duel timing and ship-handling minigames
Reads0 vs 0
Even - both lean on reads about the same.
Variance4 vs 4
Even - both lean on variance about the same.
Optimization7 vs 8
Siren leans harder on optimization: Each mission is a puzzle with a near-exact intended solution
Two games can score the same on an axis and still test it in very different ways - read each rationale, not just the number.