Not just 1871. The Austrian had a decisive advantage in numbers and artillery in 1866 at Koeniggratz in the Austro-Prussian War. And their generals threw wave after wave of their own muzzleloader-equipped infantry at the Prussian elite dug into cover and armed with breechloading Dreyse rifles like Zapp Brannigan facing killbots. Unfortunately for them, nobody's been able to discover a Prussian killbot's limit, not even the Soviet Union. To go with what
@Only an exceptional individual Sometimes said, there was no excuse for the poor showing in 1870 or 1914.
Nothing at all really, aside from having a full 1/3 of their forces either dead or wounded and having pushed the capabilities of a supply line that stretched from Pennsylvania all the way back to Virginia to its limits. His men were exhausted and low on food and ammunition, with 8k wounded that needed to be evacuated, and with his advance stopped cold the North had time to resupply and replenish its forces... a luxury Lee did not have all the way in Pennsylvania.