Not true, Just because a group of people decide to stand in one group doesn't mean that their opponents will stand in one group. This is also why ancient military tactics also included formations that help to deal with the enemy attacking the flanks.
we see similar strategy in north American football. For example, If I'm in a 5 vs 5 fight and I see that my opponent wants to attack in a ground then I'm going to have someone attack the flank. While 4 of my guys occupy 5 of their guys then I'll use my 5th man to attack. If you want to know how all of this stuff works then you have to look at some ancient military tactics.
Here an example of what I'm talking about. You'll see both the flank and isolation. 3 take the flank. 2 go out to look vulnerable. As the 3 rush one breaks from the group isolation. But once again. The group has to fight as a unit. It's not enough to be a group. There has to be coordination and communication. Even though one team split into a group of 3 and a group of 2. There was coordination and an understanding of a plan of how to deal with the other 5 and it wasn't going 1 vs 1.