Something I haven't seen mentioned about the W03 & the DDRS is the fact it allows them to run a lower ride height than other teams. Yes ride heights are controlled by the FIA, however we all know different teams do different things. Ride heights are generally set at the end of the straight so the plank doesn't get worn out because that's when the car has the maximum downforce. Mercedes is stalling the front wing, decreasing downforce thus they're able to run the car lower than other teams do and they're gaining downforce in the low speed corners.
Mercedes DDRS system is still giving Mercedes an advantage in the race as well because of fuel load & limited DRS, so you've got limited downforce anyway, so the lower ride height compared to others is still helping. People seem to have overlooked this when speaking of the system and thinking it only helps in Quali. Wrong. Ross is a very smart man.