There’s a reason modern airliners still have physical throttles.
It’s important to know, for certain, what throttle and brake input is being provided to a vehicle, and the ability to control that input without having to look at a screen.
Like the stick, the throttles control electrical and hydraulic systems. The retrofitted controls on the DDGs will do the same.
Not like the old days when the throttle on the bridge moved a nearly identical indicator in the engine room. Then the engineering officer would shout out the engine throttle.