...insight into what was so hard about SotS2 trade is really what I am looking for as I remember the TON of people mystified by it.
Ok. It's been a while since I played SotS2, but I did a bit of refamiliarization and reflection. This is a bit of a wall of text but I hope it’s valuable. I have some thoughts about why people used to SotS1 might find SotS2 trade confusing:
1) In SotS1, when you build a freighter, you are assumed to have docking capability for it. Whether this is part of abstracted general purpose orbital infrastructure or the cost of the dock is abstracted into the freighter cost doesn't matter; you can't have a freighter without a dock. In SotS2, you have to build freighters and docks separately; moreover you have to build them on different screens. So it's quite possible to build a freighter and set your I/O slider up a notch to generate a trade good, but still not generate income because you're missing the dock. Moreover, needing to build these separately increases the micromanagement required for trade, so that might have been a turn-off for some.
2) Related to (1) above, in SotS1 you don't have to go to the trade screen to get a useful result from building freighters. You can see in the main view when you select a planet that it has a certain number of ticks corresponding to the number of routes to fill, all you have to do is build freighters, and set your I/O to the tick mark you want. In SotS2, however, the trade overlay is much more central to trading than the trade screen in SotS1. Your tick marks on the main screen don't
tell you how many routes you have to fill, they tell you how many trade goods you can produce, and you have to look elsewhere (the trade overlay) to find out how many you actually benefit from producing. Some people couldn't find the trade overlay immediately, or wanted to wait to explore it until they were more familiar with the basics, and got confused as a result.
3) In SotS1, trade is its own thing and is just another way to make money via vertical development. You can largely ignore piracy if you want and just replace freighters when they occasionally get killed. Trade doesn't have a lot of interactions with other things. In SotS2, trade is tied into a lot of other systems -- not just piracy, but planetary economic development and government type. In SotS2, you can actively get punished for trying to build up trade if you don't do it "right", via rotting goods or morale effects or being pushed into a government you didn't want. But you have to be paying pretty detailed attention to various non-trade parts of the UI, and/or be reading things in the game files or on the forums, to figure out that these interactions exist, never mind how they work. This can be a big source of confusion and a turn-off to unsophisticated players who just want to make the revenue numbers go up.
4) The underlying principles of SotS2 trade are not very complicated conceptually, but because of 1-3 above, it winds up being more complicated to actually manage than SotS1 trade. However, the game doesn't really stage that management complexity increase for someone used to a less involved trade system. You just get all of it, as soon as you research FTL economics and start building freighters or trying to encourage the game to build them for you via stimulus.
So if I were doing a post-mortem on SotS2 trade, with the aim of having fewer confused players, among my take-aways might for example be the following:
A) The game shouldn't require the player to go into any trade/station screen or overlay to get a basic, positive result from investing in trade. Freighters the player builds shouldn't require separately constructed docks to function at all, but a trade station might give better docks than default abstracted ones. Key information like the number of routes that are available to be filled, and hence the number of freighters required, should be on the main screen; the trade screen or overlay should be for more details or optimization, e.g. moving freighters between possible routes.
B) The game should strive to avoid reducing positive revenue generation as a result of the player investing in trade suboptimally. The cost of doing things suboptimally should primarily be the opportunity cost of not having invested those resources better. If the game needs to make there be a consequence to doing something suboptimally beyond opportunity cost, consider treating it as an extra expense rather than a reduction in income.
C) If there are things in the game (like trade stations) that improve the range of options available for freighters, or that cause trade to interact with other game systems, consider tying those improvements or interactions to a separate tech, so that the player can opt into/out of them and so that the added complexity can be staged to an appropriate tech era.
Hopefully at least some of that is helpful.