A heat map alone does not compare two players who play in completely different positions and roles you numpty. Pulisic has the same heatmap as Mount, should we switch Pulisic to play as a #8 then by your logic? He'd obviously excel there given he has the same heatmap!
There is a reason why Grealish has excelled tremendously at LW as compared to playing in central midfield. Because he possess skills that makes him a great attacking threat. Taking players on, finding key passes in the final third, and being able to attract defenders. All of these qualities would be redundant if he'd be operating Mount's position and role, a role that sheds more responsibility in build up and transition as opposed to Grealish's role of attacking.