Quote Originally Posted by Alexanderofmacedon
Very good point. One reason Darius lost his empire in my opinion. He did the same thing at Issus.
He fled, yes. But fleeing does not neccassarily make one a bad general, and a "tactical repositioning of forces far away from the enemy" is sometimes good. I think it boils down to that Alexander was just way better.

Along the same lines, how much battlefield tactical control did Barbarian leadership have?

As most of us know, once the battle is engaged, it is extremely difficult to coordinate activities. What I primarily refer to, I suppose, is the planning process prior to engagement.

Did Barb Generals possess enough authority and inspiration to effectively cooridante quasi-uniform units in a meaningful manner? I would imagine that it would be slightly more than, "Here's a spear. The enemy is over there."
Steppe generals, and other Eastern horsemen could reform quite well and execute quite complecated manuevers. Unlike Western knights, which was more of a charge and that's it sort of thing, the reliance on horse archery neccestitated very coordinated manuevers, helped by hunting and years of herding animals with the guy next to you. Heavy horse could also stop a charge. For example, the Sassanians would send a charge of Savaran (cataphracts) against Roman infantry, which would turn aside and go back, which was followed by a wave of horse archer, who would also swerve, followed by another line of cataphracts. So yeah, Iranians, especially nomads could do a lot of complicated manuevers, more so than later Westerners.