I agree WW should not be a problem against tribal nations but need to know the source of discontent since all goods are available, lots of policing is present, and this seems to be the only possibility unless there is an unemployment dynamic or just a leftover from the loyalty situation.
Kensai wrote:The IsMajor bug is a kind of non-bug or at least a bug as you see it. It was probably in to avoid allowing minor nations venture in places it is not realistic to venture (for example a 1860s Brazilian expedition in China!

)... but yeah, I think it could be fixed. However the main feature of IsMajor=0 is that it prevents minor nations to be global players regarding trade capabilities, etc. And that's a correct abstraction, imo, albeit frustrating.
The comment is a digression in part, but anything that destroys units with transit rights if peace occurs can't be justified by any historical event so must be considered a bug in the feature.
The IsMajor=No feature also prevents minors from obtaining the normal benefits of alliance military intelligence - this appears to be designed in but is hard to understand especially since the AI minors need all the info they can get for their AI (but maybe it helps save processing time - something which would not apply for human players).
Your wise comment regarding the Taiping rebels and heretics I disagree with as it made sense in context as a basis for relations given the options available. And it is a red herring since the bug prevents as well as supply and transit into neighboring countries and ports as well as overseas.
The trade restriction is only a correct abstraction if it achieves the right effects. Historically, the US overseas merchant marine in the 19th C was weak as the resources that might have gone that way were focused on enormous internal development and transportation. The same applied to other countries focused on internal development, and these were able to rely on the world's merchant marine to effectively sell their products, which does not happen in game. The US is given a workaround by being allowed a merchant marine that circumvents the game restriction - and building its own merchant marine is what would have been forced historically if the market had been obstructed such as by a "national bottoms" treaty. The same should apply to other countries with maritime capabiltiies. So what is the basis for thinking it is a correct (i.e., unflawed) abstraction? Similarly, there were minors with extensive merchant marines that are not fairly represented by the restriction. Again, a question.
A better abstraction as you call it would be to allow countries to sell through foreign merchant marines in the destination trade box, at which point the merchant marine are just a source of revenue.
In either type of fix, force pool restrictions on merchant marine are reasonable.