Finally a counter argument I find worth thinking about it. (Unlike "lol wtf someone else walking for me? GTFO!")
Could you elaborate what exactly went wrong, next to the obvious fact that in M&B footwork is needed for fighting, which doesn't fit to the idea of holding a line in a shield wall?
In those cases we would be on one team, forming formations with shielders, a few 2h and a few pikemen. We moved in formation too, which looked awesome. Amazing to see the enemy team give way too such a large concentration. No one liked to attack 8-10 enemies on his own. It sure has an effect on morale.
In some cases the enemy started creating shieldwalls too, which made me smile, and which caused some really medieval ish battles. But in most cases the enemy wouldn't. Which was ten times more effective. The problem is that in Warband every player pretty much moves individually. So around your little formation are enemies, single enemies. What do you do if an archer starts shooting you in the back? You can't chase him, you'll be without cover in the front, if you chase him he will probably run away. As a formation you are very much a focal point for ranged. You either get shot to pieces from different directions, or you end up forming half a circle against a wall.
As soon as the enemy does attack in considerable numbers, you have to break off formation. Fighting in formation causes a whole lot of doing nothing, because people are too afraid to hit teammates. The implementation of earlier active attacks has been very effective in making teamwork shit. Derpdevs. A lot of swings glance on your teammates, we even got opponents killing three of us right in our middle because we were unable to hit him while in a close formation. We also had cav running right through our formation, while it mostly consisted out of hoplites. You are very careful not to hit teammates and you therefore react slower.
After you break off formation its very hard to get back into formation, especially if you lost players, especially if you lost shielders. People are also completely not used to fighting as a team. We tried fighting in duo's. A designated partner that sticks with you and helps you out. You even lose those in combat.
The only way I can see formations work is if you have cav support and archer support looking out for you. Some system to make people move at the same speed when in a close group would really help maneuvering as a formation. Being stuck to another player, meh not so much.