head to head
Neither is simply harder - they are hard in different places. Magic: The Gathering Arena demands more variance; Overwatch demands more execution.

Optimization · Grand Arena
A deep card game blending opponent reads, draw variance, and sequencing.

Execution · Grand Arena
Team hero shooter blending FPS mechanics with ability economy mind games.
Magic: The Gathering Arena leans Optimization (Grand Arena); Overwatch leans Execution (Grand Arena).
Overwatch leans clearly harder on execution.
Magic: The Gathering Arena
Pure clicks, no mechanical skill
Overwatch
Hero aim, movement, and ability timing
Same score on reads - which means the number cannot separate them. The difference is in what each one asks of you.
Magic: The Gathering Arena
Bluffing instants and combat tricks against humans
Overwatch
Ult tracking, flanks, and baiting human teams
Magic: The Gathering Arena leans clearly harder on variance.
Magic: The Gathering Arena
Mana screw and topdecks remain decisive
Overwatch
Minor spread and matchmaking noise
Magic: The Gathering Arena leans clearly harder on optimization.
Magic: The Gathering Arena
Deepest sequencing, deckbuilding, and stack puzzles
Overwatch
Team comps, ult economy, and positioning theory
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.