And yet the statement that I'm getting aggro for disrespecting says just that. Or, should I say, appears to me to be saying just that. If all it actually says is that X-boat routes and major trade routes tend to overlap, with no cause and effect involved, then I'm fine with it.
As far as I can tell, the citation that touched off this entire discussion is from The Traveller Book, at the bottom of page 150:
Xboat Routes: The heavy lines connecting several worlds are express boat routes providing communications between worlds of the Imperium. These routes are also common trade and transport routes with regular commercial transportation provided by one or more transport megacorporations. Service to locations not on these routes is less frequent and less dependable.
Note the use of "also", which which is used to append additional information without indicating a causal relationship. My read of this statement is that X-Boat routes and trade routes commonly coincide, but no cause-and-effect connection is explicitly stated or implied.
Other Traveller canon material makes it clear that the trade routes came first, and subsequently "selected locations along major trade routes are established as express stations" (Supplement 8, page 26). There is no information on what the selection criteria were. From the available evidence, I would suggest it was more political than practical, resulting in a system that overall averages less than J-3.
The X-boat network was designed to tie together the Imperial bureaucracy. That means the primary links going from subsector capital to subsector capital, not major trade world to major trade world.
Yes - as you point out, even by this criteria the network in the Marches doesn't make a lot of sense. I suggest that the in-universe "reality" is that the Imperial charter for the X-boat system was to tie together the subsector, sector, domain, and Imperial capitals by establishing J-4 links along major trade routes.
In between, worlds with major political power would be lobbying for their own X-boat links, and worlds with political power will often be worlds with lots of trade, but that's not quite the same thing.
Yes, and rather than play politics or push back, the Scout service (which has always been the least politically well-connected of the Imperial services) decided to appease almost everyone. The result is that political forces have been able to distort the network to the point where it arguably does not actually meet its charter. This distortion is particularly evident in the frontier regions such as The Spinward Marches.
IMTU, Scout officials in the Marches readily agree that the network makes little sense, but claim that their hands are tied: The IISS has no budget to establish new links, and it is politically impossible to re-route existing links due to long-standing opposition to such changes by the Duchess of Mora and other nobles allied with her. It is interesting to note that the existing network places Delphine of Mora close to her allies in Trin and Lunion (6 weeks from Mora) and to the Domain capital (10 weeks from Mora), while isolating her primary rival near the end of a long branch of the network (Regina is 22 weeks from Deneb and 12 weeks from Mora). This puts Norris in an interesting position: either he can govern from Deneb and put Mora in a position to meddle in Marches with a relative free hand, he could govern from Regina but have to deal with long communication delays, or he could govern from Mora where Delphine has her power base. But that's just IMTU.
The canonical X-boat links seems to have been established by random die rolls
Agreed. In the 1977 edition of Book 3, there are rules and a table for determining jump routes between worlds, at the bottom of Page 1 and the top of Page 2. Routes are based on the starport types of the two worlds and the distance of the Jump (from J-1 to J-4) and a die roll, resulting in effectively random routes. I suspect that a version of this approach was used in creating the Spinward Marches.
The revised (1981) edition of Book 3 and The Traveller Book instead put the entire process in the referee's hands. These rules state that "Within the subsector, local governments will have established communications or trade routes connecting some (but not all) worlds. These routes serve as a conduit for messages between businesses and between governments as well as between people. They also serve as the basic routes that liners and large freighters travel. The referee should examine the subsector map and connect key worlds with communications routes." (TTB, page 81). Presumably this approach was used for The Solomani Rim, and the routes arguably make more sense.
Traveller5 introduces a new procedure, where you calculate Importance based on starport type, tech level, trade codes, population, and bases. The world with highest Importance is the capital (number of trade codes is used to break ties). All Important worlds (typically Starport A or B, TL-10+, Population 7+, and either military bases or some combination Ag, Ri, Hi, or In) are on the X-boat network; the referee is responsible for designating links, possibly via less-important worlds, to ensure that all of the Important worlds are on the network.
Overall, I think that the T5 approach is the best of the bunch. Done well, generation using this procedure should make X-boat routes roughly align with trade lanes (and I presume this is the overall goal). It is still pretty subjective (and still leaves us with a Spinward Marches map with some very weird X-boat routes).
Meanwhile, the IN's jump-6 couriers must have been beating the X-boats like a big bass drum since 1000 (and their jump-5 couriers must have been outperforming the X-boats since 700). That nine-link route from Rhylanor to Regina is a two link route by "NavyNet".
Agreed, and this is definitely canonical. There are multiple references in MT that key Navy officers and political figures would be informed of important developments well in advance of the public notification through the X-boat network.