Its a dead stat that only increase walk speed, strafe speed, and increases the distance traveled[be it X or Y axis] of the first jump only[does not effect second or 3rd jump]. & decreases movement speed the higher your mobility for titans & warlocks.
Making it increase it sprint speed would be the best option as this would benefit all 3 classes. Lets be honest its weird 2 of the classes gain movement bonuses for suppressing the stat, while the 3rd class only gains a class ability CD reduction for investing into the stat but no movement bonus.
[i]Edit: For the 1millionth time, mobility currently does not increase your sprint speed.[/i]
THE PROBLEM IS that Titans can skate faster than sprinting. They have unlimited and a BETTER dodge with the melee ability, that in case of panic, can one hit kill from 10 meters away in a blink of an eye. They can have 100 resilience, with Max flinch resistence, AND 100 recovery WITH some nasty life and shields regen on TOP. They got It ALL, better than everyones else.