I think its important to consider on a more general basis, is "how multiplayer friendly do we want all civs to be?"
Here's what I think about that question: We need to establish what civ that has the maximum tolerable exposure to other players. What single civ is very dependent on other civilizations' performance and choices, but still within tolerable limits?
I would propose the two possible candidates are
Assyria and
Siam.
To a certain degree, any diplomatic or military civ is pretty exposed to counterplay by another human. In multiplayer, military victories are hard, but DVs are virtually impossible, because human players can coordinate and plan votes very well. Other humans can make the threshold for unpopular proposals prohibitively high. However,
Siam is the closest thing we have to a "pure" diplomatic civ, which also makes him the most predictable and easy to counter by other humans. Also, Siam has more bonuses for DV allies, but doesn't actually have any in-built tools for getting more influence with city-states (at least until the next version is released, but even that new bonus is modest). He's almost pure win-more, unlike other diplo civs like Greece, Austria, and Germany, who all have some in-built extra influence mechanic. This is a very vulnerable position to be in vs. other humans, who are cognizant of what you need to be able to play your civ.
Assyria's big UA power is a reward for city conquest. That means you have to conquer, which means you have to win wars against other humans. Conversely, all the other human players have to do is not lose cities to you, and Assyria is playing with only half his UA. Assyria is helped by large, early science bonuses, and has various tools to get an early tech and military lead, but there is still the possibility that he can be entirely shut down.
There were two old civs that were also very hard to use in multiplayer, but have since been changed, or are going to be changed soon:
India and
France.
India's old bonus for passive spread made his religion incredibly brittle. If enemy human players knew what they were doing, they could coordinate missionary and Great Prophet spreads into India early, before his passive spread became insurmountable. Human players know from the game start that India is on the map because they get a global notification about a pantheon founding at turn 1, so they have lots of time to prepare and plan too. An India player has no way to defend themselves against this until they have enhanced, and even then they will spend a lot of time trying to turn their own cities back. In the meantime, India functionally doesn't have a UA. This is being changed next version so that India's Gprophets give human players more control over where and when they spread. I think that should mostly address India's lack of counterplay up to this point.
The old
France was like Assyria, but on crack. He had even larger rewards for city conquest and even fewer bonuses outside of that to actually help him conquer. His other components were weaker and later than Assyria's. He has now been changed so that his bonuses are much more self-contained, and less dependent on winning wars.
In summary:
- Assyria and Siam are tolerably exposed to sabotage by other players.
- There used to be two other civs whose kits were even more at the mercy of other players -- France and India -- but we changed them.
- That just leaves the Netherlands as the only civ that is more exposed than Assyria.
That's why to me its gold saving that is the primary UA, and the debt that is the possible "vestigial" ability.
[...]
And that is the strategic decision turn after turn, when do I off ramp? Do I keep saving for even more gold, do I spend it now for infrastructure that will also help me later? How much do I hoard and when I do spend, that is the strategic decision you are adding to the game.
Considering how espionage works, and how it will continue to work for the forseeable future, hoarding gold like that is simply not viable. If you try to do that, other players will treat you like a piggy bank to be smashed over and over. The ability would need to be buffered anyways so that it isn't just stale, and you don't feel punished for buying things, but I would consider it completely off the table unless the ability also had some way to prevent enemy spies from simply taking all of your gold.
I think the Netherlands would still be very good in MP, players simply don't work together that well to block their ability. You need everyone to turn down literally free lux.
Even then, your ability becomes "Pay three times as much for any trade deal". Other civs' UAs aren't at the mercy of other players to make their abilities work. They don't have to debase themselves like that just so they can use their own mechanics.