Part of it is just personality type. Some people can ignore stuff they don't want but I get all OCD over thinking
- alpha systems could logically build either lots of ships or very big ships
- if systems are like earth nations then trade will be very dense
- naval density would likely follow trade density
and that led to a 3I with no firefly space inside and yet the Firefly feel implied in the early CT adventures is what I like.
So for me changing the trade concept fixes the problem - if 99.99% of the trade in a sub-sector is concentrated in a dozen systems in the sub-sector then 99.99% of the navy can be concentrated in those systems too.
But like I say it's only a problem if you have that way of thinking.
Well here this all comports with the OTU, as I understand it. You
can't make money with a small ship just hauling freight; on the high volume routes, the (evil!) megacorps have it all tied up. That's why it's a "Free Trader" not a "Free Freighter."
The navy (if we are including system and even planetary, who are more "coast guard") I agree follows the trade. The pirates avoid the navy. That is why you have on the original LBB2 starship encounter tables no pirates in A & B systems.
In the big systems, you have most of the cargos already spoken for, but since there are a Lot more cargos, there is always something to be bought in speculative trade. You have a (based on trade volume) disproportionately high chance of getting a good speculative cargo in a backwater world, because more of the trade is based on free traders wheeling and dealing, rather than a huge volume that is "shipped" in as cargo.
Opinions can differ (needless statement of the week!), but I buy it. Free Trader's gotta trade. He can trade on the "central planets," because there are always crumbs that fall from the master's table; often to increase the odds of making a big score on speculative trade ["..no bobbley-headed doll caper!], he needs to take a cargo from the core to the rim, where the pirates be. Again, LBB2 starship encounter table, the original spec trade rules, all this worked together, and LBB5 did not change it; indeed, it made it more believable, why MORE cargos weren't available on the High Pop worlds, like orders of magnitude more. The Free Trader is often better off on the high pop A/B starport worlds. But if the Free Trader is looking to play fast and loose with the law, ["..and where there ain't sensors, there's Feds..."], then these comfy planets are downright dangerous, because the "navy" follows the trade, even if ["...our best job was on a core planet."]