The beautiful thing about gearing is that you don't need it at low speeds and low gears. 4th gear at 600 lb/ft of managed torque is still more than 900 lb/ft in 6th gear at the rear wheels. I would guess that full power is available in 3rd-6th, maybe 4th-6th at the very least.
So yeah I think it means a LOT even with torque management. If you want 900 lb/ft from a LD or MD drivetrain you are going to have to have torque management, it's just the simple fact of life.
I am more curious about the horsepower numbers as the '15 Cummins is lowest on hp of the big three. More torque means more hp at the most used rpms but more peak hp has more hill speed potential... before anyone says anything I am not saying we need to tow faster or that the current 6.7 is weak simply an observation on horsepower as it is a very important number as well especially since you cannot multiply hp thru gearing.