This does not follow. Ships with lower jump numbers can cross a five-parsec gap. It just takes longer. There's a canonical example of an ihatei fleet of jump-3 ships that takes a year to cross the Great Rift.Originally posted by Valarian:
Aslan
jump-1 -1999 (MT Imperial Encylopedia)
jump-5 -1014 (Alien Module 1 - Aslan)
discovery of jump-5 route so presume they have the capability
Excepting the Darrians, I have the feeling that the Imperium got J4, J5, and J6 before anyone else, but I don't think that's been canonical established anywhere.
Hans