Something Trinidefender thought me: The flexing indeed looks localized in the upper flaps, but you have to project this on how the camber of the overall wing changes:
In the above picture I drew 5 aerofoils making up one single front wing. The first 3 elements from right to left are considered main plane elements and shouldn't be considered to flex. The last 2 elements are the upper flaps. I drew 2 scenario's, the one below is in normal state, while the above has the upper flaps flexing.
If we draw a red line around all of the elements in the shape of one big aerofoil, one can notice that the upper front wing has less camber and less AoA. This wing will both produce less downforce, but will also work more consistently on higher speeds (it is less prone to stall). This will give higher top speeds along better stability.
Stalling is a fickle thing: you don't want your wing stalling right in the middle of a high speed corner. In a corner like Pouhon (Spa Francorchamps) that'll guarantee lead to a trip off the circuit. Reducing overall camber is a better idea since the wing will probably stop producing more downforce the faster you go, but will not stall and drop the downforce away.
We've seen in the past with things like passive stalling systems that the point of stalling is very difficult to control. I think this is ironically a safer solution then when teams are forced to actually move to flexing the wing to stall it. The FIA should have been more considerate on that front.
