I can buy the ability of the Gepard to shred soft vehicles and AFVs but I still say taking out a tank would require a lucky hit in a poorly defended area (e.g engine compartment, attacking from the rear).
Your statement about the A-10 isn't actually correct. Trials of A-10s going against MBTs showed that the results really weren't that great. The one thing the A-10 has going for it is that it pumps a lot of rounds downrange very quickly (muzzle velocity is well over twice that of the Gepard), which means an initial round that creates some damage may be followed by a second or third round that can at least disable the tank. I wouldn't bet on the Gepard, shooting just 40 rounds at less than half the muzzle velocity of the A-10, shredding any T-72 that's coming towards your position...again, from the rear is a different story, but against the main armour I just don't buy it.