Exactly. *Everything* depends on astrography and economics of the worlds involved. Two hi-pop cosmopolitan worlds J3 apart are almost certainly going to have J3 commercial traffic between them, along with J1 and J2 traffic via intermediate worlds for passengers and cargo that value price over speed. Consider that I could conceivably get from Los Angeles to Shanghai tomorrow if I were willing to pay a huge price penalty for my late ticket purchase, while the TV set in my living room likely got from Shanghai to LAX on a container ship that took weeks to cover the same distance.
Given the tech infrastructure and astrography of the 3I circa 1100, I'd guess that ordinary commercial traffic in most regions tops out at J3. Sparse areas with worthwhile worlds will have (more or less) dedicated J4+ ships serving them. And the 3I's equivalent of the Concorde will be exceedingly rare J5-6 passenger liners, charging "If you have to ask, you can't afford it" fares.