Thx for your input on my issue.
The reason for my question orginally came from reading the FAQ. In the DotF-FAQ is stated that a pinned squad may operate an AT-gun when a friendly officer is present (although at half firepower). My idea of the desperate defenders card was that it works as some kind of friendly offcier in the squads, granting the same bonuses (allowing to operate equipment and make a concentrated attack both at halffirepower)
But when reading your comments and several rereading the op card i tend to believe your interpretation is correct. And for that it only grants the concentrated attack "bonus" to the friendly squads.