I'm going to attempt to explain the problem with Poland's UA, in a way that explains why Poland isn't just bland and uninteresting, but disrupts the very foundations of this game--strategy.
Civilization 5 is a strategy video game, but it is unique in that each playable civilization is different with unique and synergizing features that encourage and reward a unique strategy.
Some people have tried to paint Poland as a "beginner's civ." That Poland is a good starting place for players new to Vox Populi. But if someone is new to Vox Populi, shouldn't they just play on a lower difficulty? Why shouldn't the social policy boost simply be something given on settler difficulty? Why does it have to be a civ?
This also implies that Poland is a crutch civ--and in that case, does that mean Poland shouldn't be allowed to be randomly selected by the AI in singleplayer? What about multiplayer? After all, if everybody is supposed to be on the same difficulty level and every civ is supposed to be balanced, is it fair to be forced to play against a crutch civ? To potentially lose to someone, not because they are better than you, but simply because they are playing a better civ?
You may counter this by saying that Poland is weaker than other civs--that it's strength is given by its flexibility: this is true. There's nothing wrong with a civ being flexible; but Poland is fundamentally broken because its flexibility is UNEARNED. Allow me to contrast Poland with my current favorite civ: Carthage.
Carthage is an incredibly flexible civ--if you play them right. Carthage's flexibility comes from their riches. But their riches do not come from thin air, they are granted by settling cities. Carthage gets a free lighthouse in every naval city, which rewards coastal settling and saves you maintenance. Carthage also gets a trade route buff and a unique wonder which further buffs trading. You can say everybody builds trade units (I disagree, for warmonger civs, trade is a much lower priority as trade units aren't often worth the production as they will simply get raided in the next war), but this fundamentally changes how I play the game. The trade route bonus makes me much more reliant on trade partners. It makes me lean towards avoiding war with trade partners.
"But," you're probably asking, "everybody avoids war with trading partners. So, Carthage doesn't change your strategy." Wrong. I don't generally avoid war with trading partners to the same extent of Carthage:
While I was reading this thread, I realized a fundamental problem with people's understanding of Civilization balance. Somebody in this thread earlier mentioned how Zulu could be considered "flexible," as the gold maintenance saved could be used to maintain a cheaper defensive army and the money invested elsewhere. Everybody compares a civ's unique features to a blank, vanilla civ without any unique features (I like to call them "city-state civs"). But this is wrong. Because, in Civilization 5, you are not playing against city-state civs, you are playing against other civs with other unique features. So you're not playing a civ just for passive bonuses, you are constantly trying to maximize the bonuses from your unique features, because that's what everybody else is doing.
So, if I fail to utilize Carthage's trading bonuses to its fullest extent, I will not be punished by some in-game feature, I will be punished by other players/AIs, who are better and more intelligently using their civs unique features to get ahead. How do I maximize Poland's unique features? At most, I might select a different tech to get to the next era faster and I get a better bonus from horses, so I am more inclined to settle near horses. But... that's it. Poland's flexibility is otherwise granted for free.
Let's summarize: Carthage is a wide naval civ that more strongly rewards trading. Poland is a flexible civ that can pursue any general strategy. Perhaps you've already realized the problem.
If I wanted to counter Carthage, I might avoid settling naval cities, unless I'm confident in the production of my naval cities to outproduce Carthaginian navies or perhaps I will build an army to target Dido's Achilles Heel. If Carthage begins to get too wealthy/powerful, I might declare war on them and raid their trade routes to prevent snowballing. Because you're not just trying to best use your own civ's unique features, you are trying to counter other civs' unique features. You have the goal of attempting to outplay other players/AIs and undermine their civ's bonuses. This is a strategy game and there can only be one winner.
But, how do I counter Poland? Whenever I play against Poland, the most I can do is check up on their social policies to get a VERY VAGUE feeling about what strategy they're pursuing (which I already do with other civs) and I am inclined to steal horses from them so they cannot use their UB and UU.
Poland being vanilla without any unique strategy doesn't just steal the opportunity of a unique experience from those who play it, it STEALS the depth of strategizing in a STRATEGY GAME from other players. In that regard, Poland's UA is completely broken by its very concept and is ANTI-STRATEGY. It is not fit in a strategy game like Civilization 5.