Thats true, but true for everything, thats more of a factor of battle than a fault on their part (although its true they are less mobile), anything can get surrounded and cut off (even though the AI isn't usually that bright)

As a unit though its pretty tough, i usually have quite high experience ones aswell because of the amount of line grinding they do. That said i still do prefer mounted generals also, i like the KH merc generals for this.