scanning thru the article:
"God of the Open Sky" is one of the more popular ones by the AI to choose; it's in love with culture only pantheons.
Also it seems that I get starts with fewer horses/cattle/cows on average playing Poland than with other civs.
I see a reference to caravans: Build cargo ships instead if you have a coastal city.
Policy references: I wouldn't open Honor until finishing your intended first tree even with Poland's faster policy rate. The tradition / liberty / piety finishers are all much stronger and you want whichever tree you chose ASAP.
I'm surprised Piety isn't mentioned. Poland is the one civ best suited for a full Piety tree first start as it will have time to finish Tradition second before Rationalism.
Rationalism should also be mentioned as well in that sectionl as it's the best tree for all civs, including Poland, for all forms of victory.
Parthenon: I'd skip that as there isn't a theming bonus attached. Oracle though is good.
Cultural section: Opening Exploration should wait for Industrial. (Louve isn't available until the Industrial era.) Exception if you haven't met everybody yet and so want Exploration opener's normal benefits.
I'd also add Globe Theatre to that list; it's shaky on Immortal but other than Oxford is the only source of literature theming bonuses.
The scientific victory section appears to be assuming a self founding wide empire.
If going 4 city tall; you're better off with other policies after Tradition while waiting for Rationalism to open.
One possibility is take by Consulates (increase city state resting point by 20 points), top right of Exploration (happiness from naval buildings) and opener of Aesthetics. (faster great guild specialists). And as Poland you can get all that in the same game without slowing down Rationalism.
Diplomatic victory: The city states with barb camp requests always reveal where the camp is; no need to open Honor for that.
Yes, Rationalism is great. But before you can open Rationalism you may be able to get quite a few more policies within Patronage as Poland.
AI: Gets a 25% research handicap even on Settler. I think it's the population growth handicap you are referring to there as that's the ongoing one that grows as the difficulty level increases. But you may also be referring to the AI starting handicaps.
Poland peaking in mid game??? Only in hands of dumb AI. In hands of a human they'll build on the success they've already achieved.