If ships that big break formation in a convoy chances of getting them all out alive are low. They would collide or scatter like stampeding cattle. In the main hyperspace routes you hope there is enough traffic to answer a distress call. If you are risking the outer rim with big, unarmed ships, you are either a rebel convoy, illicit, or hoping to make a big payoff on a risky venture. Whichever it is, you had better pack enough of an escort to fend off predators.
Hmmm...not something I've ever looked into, but wonder if there are any WW2 Convoy simulations that might offer some pointers about approaches to game play ???