head to head
Neither is simply harder - they are hard in different places. Call of Duty: Modern Warfare 2 demands more optimization; Mini Royale demands more variance.

Execution · Competitive PvP
Blockbuster 2009 sequel famous for killstreak chains and frantic multiplayer.

Execution · Competitive PvP
Battle-royale gunfights testing aim and positioning reads under loot randomness.
Call of Duty: Modern Warfare 2 leans Execution (Competitive PvP); Mini Royale leans Execution (Competitive PvP).
Call of Duty: Modern Warfare 2 leans a little harder on execution, though the gap is small.
Call of Duty: Modern Warfare 2
Fast time-to-kill rewards raw aim and reflex
Mini Royale
Aimbot would dominate every toy-soldier firefight
Call of Duty: Modern Warfare 2 leans a little harder on reads, though the gap is small.
Call of Duty: Modern Warfare 2
Outguessing human rotations and flanks
Mini Royale
Fifty human players to predict in positioning and pushes
Mini Royale leans clearly harder on variance.
Call of Duty: Modern Warfare 2
Spawn flips and killstreak randomness
Mini Royale
Loot spawns and circle placement shake up every match
Call of Duty: Modern Warfare 2 leans clearly harder on optimization.
Call of Duty: Modern Warfare 2
Killstreak economy, loadout and map knowledge
Mini Royale
Drop spots and loadout knowledge form a thin solvable layer
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.