head to head
Neither is meaningfully harder - they pose close to the same test. The widest gap is reads, and it is a single point.

Optimization · Grand Arena
Diesel-punk CoH-style RTS with mechs and infantry cover.

Optimization · Practiced Mastery
Classic RTS that polished Warcraft's formula with naval combat, air units and beloved multiplayer.
Iron Harvest leans Optimization (Grand Arena); Warcraft II: Tides of Darkness leans Optimization (Practiced Mastery).
Same score on execution - which means the number cannot separate them. The difference is in what each one asks of you.
Iron Harvest
squad micro and cover
Warcraft II: Tides of Darkness
Faster micro across land, sea and air units
Iron Harvest leans a little harder on reads, though the gap is small.
Iron Harvest
MP flanks vs humans
Warcraft II: Tides of Darkness
Multiplayer scouting wars and build feints
Warcraft II: Tides of Darkness leans a little harder on variance, though the gap is small.
Iron Harvest
fog of war
Warcraft II: Tides of Darkness
Fog of war conceals enemy tech and armies
Same score on optimization - which means the number cannot separate them. The difference is in what each one asks of you.
Iron Harvest
build orders and unit comps
Warcraft II: Tides of Darkness
Refined build orders and upgrade timings are studyable
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.