Time for physics ;). Torque is the product of force applied and the force’s distance from the axis of rotation.
τ = r x F
r: displacement (i.e. distance between torque point and force point)
An increase in either translates into an increase in torque. The same principle underpins how levers work, or why wrenches with a longer handle are easier to turn. For screws, this means that torque is the product of the force used when rotating the screwdriver and the blade size which determines the distance of the applied force from the axis of rotation (being half the blade length as force is applied on both sides of the blade). You can further modify this by reference to the angle between the force applied and the axis of rotation, e.g. a screwdriver not held perfectly vertical won’t be as efficient.
So, as far as I can tell, the shape of a screwdriver’s profile will have zero effect on torque unless it modifies either a) the force applied or B) the distance between that force and the axis. A hollow grind changes neither directly.
Personally, the benefit of a hollow grind would be that it better fits the screw and helps prevent slips and screw slot damage. A screw slot is cut parallel so a hollow grind blade will engage for the fill depth of the slot maximising friction on the sides (i.e. grip). A flat angled blade will only contact the top of the screw slot’s vertical sides so engagement is minimal, with reduced friction, making it more likely to slip. A hollow grind would also reduce the distance between the screw slot and blade at the bottom of the slot – which also reduces the chance of slippage or weird angled rotation axes which might cause damage to the screw slot or reduce torque (i.e. hollow grinds can indirectly increase torque if you were holding screwdrivers off vertical habitually – the gain would be minimal however).
The above also explains why using the right screwdriver size is important, the longer the blade, the greater the torque you create, for the same amount of force applied. Screw slot size is doubtlessly chosen in watches to take advantage of this.
I now return you to your regular programming… ;)