More than evidence? Give me evidence. Cavalry can widen the space of encirclement allowing Legionaires to route hoping to escape but still keeping the encirclement closed.
Except two historians disagree that the cavalry could have prevented infantry from escaping. And it is evidence if they did get completely annihilated that Hannibal would have probably not entirely surrounded them.
Have you seen what happens when armies are surrounded on open ground? It becomes a Pyrrhic victory.
Stalingrad not open ground? The escape route was a steppe (where the two pincers closed and where Mainstein wanted to attack). The city and Volgra river were not open ground but this wasn't the enemies line of retreat.
No, Stalingrad was not open ground. Sun Tzu even describes what open ground is.
Sun Tzu fought in a time of swords and compacted field armies not landscape stretching miles and miles encompassing rivers.
Most of the battles of Sun Tzu's time were not compacted field armies.
Again you haven't rebuted the fact Sun Tzu's methods can can't you horribly annihilated as Varus did.
Except I did. You're not even understanding Sun Tzu's principle that you're attacking. He does not say to let the enemy retreat. He says to show them a way of retreat so that they think there is something better than death, and then to strike them. Instead of fighting what is essentially a "cornered animal", you can defeat a force with far less effort.
The entire purpose of Sun Tzu's quote there is to avoid Pyrrhic victories. Not to let your enemy escape. i.e. "If an enemy is presented with a way to escape, he will take that as opposed to fighting to the death. Then you can destroy him with ease."
Understand Sun Tzu before criticizing it.