head to head
Neither is simply harder - they are hard in different places. Heroes of the Storm demands more execution; Minion Masters demands more variance.

Reads · Mind & Math
Objective-driven MOBA with shared team XP.

Optimization · Mind & Math
Real-time deck duels testing counter-play prediction against draw-order variance.
Heroes of the Storm leans Reads (Mind & Math); Minion Masters leans Optimization (Mind & Math).
Heroes of the Storm leans clearly harder on execution.
Heroes of the Storm
Skillshots and rotations require hands
Minion Masters
Placement timing matters but inputs are simple
Heroes of the Storm leans a little harder on reads, though the gap is small.
Heroes of the Storm
Team-fight cooldown trading is prediction
Minion Masters
Live human opponents bait, counter and adapt each match
Minion Masters leans clearly harder on variance.
Heroes of the Storm
Map objectives and merc camps vary
Minion Masters
Card draw order decides what answers you hold
Same score on optimization - which means the number cannot separate them. The difference is in what each one asks of you.
Heroes of the Storm
Talent picks and team comps deep
Minion Masters
Deckbuilding and mana-efficiency math drive the meta
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.