I mean, milage always varies of course. I'd argue if you're turning on a dime that often with Reinhardt, your team isn't really doing their job protecting your flanks. And his fireball is big enough that is don't miss mouse aiming with it. And the extra range of movement a control stick can provide over keyboard movement could potentially trump quick turning, especially on a melee based character. I have a better time keeping my shield at the right angle with the extra range of movement only a controller can provide.
I just like having the option. You even have fighting game tournaments where the occasional person uses a controller rather than a fight stick and succeeds. Overwatch is balanced better than most shooters for controller use vs. Mouse at the very least.