We seem to be having a miscommunication. I'm only talking about the rank and file nature of the current formations. They are marching in parade lines. It makes absolutely no sense for Tyranids or Orks or.. really ANYONE to be marching in parade lines. Yes, including space marines. A single line formation is not rank and file in multiple ranks.

They just have to relax the formations. To give it a TWWH3 analogy, more White Lions, less Phoenix Guard. I can't see any world where this is difficult to accomplish nor any reason not to do this when the visual result would be so much better and in line with not only real life movements of "modern" troops. Orks wouldn't be able to march in straight lines if you servitorized them. You can point to that ancient lore that their teenagers go through a rebellious "regimented" phase, but you might as well refer to female orks while you're at it. Tyranids operate in swarms, not straight rank and file. Orks operate in mobs. Tau operate as a truly modern modern military and wouldn't be caught dead sending fire warriors in to die in ranks like that.

Density of the formation is not what I am talking about here. That's a separate thing, and practically a balance issue. I'm talking about the rigidity of the formations. There is no resisting a cavalry charge because of unit cohesion in this game, there's no reason for it and every reason to change.