Hena, I actually believe that the tyranid swarms are highly organised, but such organisation is hard for the prey creatures to see.
The current list allows you to buy lots of units then stick them down wherever you want, within synapse range, however, most swarms are placed in ways similar to my suggestion, which removes a special rule (swarm organisation).
Massive Carnifex broods are always supported by a Tyrant or two, or sometimes a mummy beast.
If you have a load of Trygons and Heirodules then you would either spread them out to provide support multiple swarms or group them around the dominatrix to soak firepower.
You wouldn’t have a tyrant leading a massive gaunt swarm or the node babysitting Trygons.
It also allows us to have cool sounding names for our formations
Endless tide for a tyranid warrior formation
Crusher brood for a tyrant lead carnifex brood

? brood for a tyant lead artillery brood (tyrant brood with 0-4 exocrine/dactylis and 0-2 carnifex/malefactor/haruspex)
Behemoth brood for a dominatrix and her gaggle
Winged horror for a Harridan lead swarm
Infestation for a hive node