I think (although not sure) that, with the advent of CGCC computers and in order to save fuel, that new big jets suffered a slight redesign of the stab profile. New jets are not designed to be stable. They are designed to fly with near zero trimming. It is therefore a waste of lift and fuel, to design stabs producing negative lift, together with 5 Ton of Fuel...
[my highlighting]
True that many jet fighters are fundamentally unstable, but it does not apply to public-transport jets (yet...).
The FBW-controlled A320 is not much less stable than a B737, as far as I know. And it is therefore flyable, and just about land-able, using the THS and rudder as the only means of control. (We practise the former on the aircraft, and the latter in the simulator, on initial conversion.)
The (up-to about) 5 tonnes of fuel in the A330 THS is moved there purely to relax the stability slightly in the cruise, and reduce the negative lift required of the THS (for the reason you stated).
Re the THS bottom-surface camber, I can only speak for the A320. The best view one gets is from a set of steps, when they are positioned at a rear door. The leading edge area is then clearly visible as having more bottom camber, What happens further aft is less clear, I must admit, but the top surface does not show very much convex camber.
Not sure all this makes much difference to mm43's graphic!