I've been following the FCS program pretty closely. From everything that I've read the weight of Manned Ground Vehicles was to be 24-28 tons. They gave up the hope of transporting them in C-130 Hercules and chose to up the armour a little. You also have to remember that some of the reduced weight is due to other factors than armour reduction. The rubber tracks weigh less than the old steel tracks, the remote weapons turret weighs less the current turret, the hybrid-electric engine weighs less then a conventional engine, the lower fuel requirement saves weight. So when you compare them to the vehicles that they are replacing they basically weigh the same and offer just as much protection. They are to protect against 30-45mm cannon fire over the frontal 60 degree arc and agains 14.5mm and 155mm shell fragments on the whole vehicle. That's pretty much the same or better than the vehicles that it is designed to replace, with the exception of the MCV variant vs the M1A2 Abrams. Then the active protection system protects against higher calibre rounds and anti-tank missiles.
M2 Bradley Infantry Fighting Vehicle 30 tons
M3 Bradley Cavalry Fighting Vehicle 30 tons
M109A6 Paladin Self-Propelled Howitzer 32 tons.
M113 Support Vehicles 12-13 tons (Command Post, Medical & Mortar Carrier)
M1A2 Abrams Main Battle Tank 70 tons
M88 Armoured Recovery Vehicle 70 tons (but the weight is only for recovering the M1 MBT not for protection)
So in the end the FCS ICV and RSV variants provide basically the same protection as the Bradley IFV and CFV variants they would replace. But they carry more infantry (9 vs 6 in the Bradley), more scouts and recce equipment (4 vs 2 in the Bradley, plus various surveillance systems), they travel faster and quieter (90 km/h vs 66 km/h for the Bradley) and have a better unrefuelled range (750 km vs 483 km for the Bradley).
The support variants of the FCS: Command Vehicle, Medical Treatment Vehicle, Medical Evacuation Vehicle and NLOS-Mortar are actually much better protected and much better equipped then the M113 variants that they would replace.
The NLOS-Cannon, which has already been completed, is equal in fire-power to the M109A6 Paladin, it is lighter but it has a crew of only 2 vs 4-5 on the Paladin and it is much faster (90 km/h vs 56 km/h) has a much longer unrefuelled range (750 km vs 350 km) and is much more digitilized, including an auto-loader capable of faster fire than the Paladin.
The only big issue is the FCS Mounted Combat Vehicle that would replace the M1A2 Abrams Main Battle Tank. It weighs less than half the Abrams and completely relies on Active Protection to defeat enemy tank rounds and anti-tank missiles. However, its still faster and quieter (90 km/h vs 68 km/h), it uses considerably less fuel (the biggest drawback to the Abrams is the massive fuel consumption) which gives it a bigger range (750 km vs 391 km) and its 120mm cannon is the same size as the Abrams but it has a non-line of sight range of 8 km vs a 4km for the Abrams' M256 cannon. And of course the M88A2 Armoured Recovery vehicle has to weigh the same as the Abrams in order to recover it, but the FCS Mainteance Recovery Vehicle only needs to weigh 24-28 tons and has the same advantages in speed (90 km/h vs a very low 40 km/h for the M88) and carries more mechanics than the M88.
So when comparing the FCS MGVs to the vehicles and systems they would replace I don't think its such a huge mistake. They seem to have similar protection other than the MCV/M1A2 Abrams. So if the only issue is the MCV maybe only it should be re-evaluated? The US Army claims that the new Stryker ICV is highly successful in Iraq and the Canadian Army has been successful with the LAV-III in Afghanistan and they are both lighter and have less protection than the FCS would. So what is the huge problem?
Just my 2 cents.