Based on what we've seen so far, am I the only one thinking Colonization (Economic Policy; +50% to settler production) is game-changing, and will be the optimum strategy in pretty much every game? Every government has an economic slot, and expansion should be the first focus (after some exploration to find the best sites) in pretty much every game. Thoughts welcome.
You're insinuating that settler-spam is an optimal strategy, which certainly wasn't the case in civ5. I dispel the notion that the +50% settler production was a good policy in a bad tree. In fact, if I could only choose one policy to run from that tree, that would be far from my first pick.
Understood - which is why I called it "wild speculation", but it does seem overly powerful based on what we know.
Considering that we know nothing - no, it doesn't. You ask why someone would pick +1 production in all of their cities over this? Well for starters your ignoring yields entirely. Now, Xian in that video displays a production of 5, which we can't be certain is an accurate depiction of a real game... but since you want to do the "what we know" approach. 50% of 5 is 2.5, so yes that is better than +1. But what if you have 2 or more cities?
You need to consider the empire you're dealing with. I can't hardly remember any game of civ since civ4 at least where I've bothered to build more than 1 settler at any given moment. If I have 3 or 4 cities, I'm not going to build 3 or 4 settlers all at once.
Later in the game, the city has a production value of 11. So you can have a 50% bonus to settlers, or about a 10% bonus (in that city) to
any production; that same bonus applied to all other cities, but the % changes depending on the yields. So if you have a newly constructed city that let's say has about 3 production, that +1 is now a
33% increase to all builds.
33% to all builds seems stronger than 50% to settlers. Furthermore, your 50% settler bonus is
utterly wasted any moment that you aren't constructing a settler. So for every turn you aren't building a settler you're suffering lost production.
So in an empire of 4 cities, where your capital has 11 production, Building a settler in the capital nets +5.5 production per turn. For every turn you build a settler in your capital, and nowhere else, so compared to Urban planning you're losing 3 production per turn across the empire . If you had Urban Planning instead of colonization, sure, you're losing 4.5 production toward the settler, but in terms of bonus production generated across the empire you've gone from 5.5 (for just one build) to 4, so you're really only losing 1.5 production toward everything you're trying to accomplish from your empire in that timeframe. Such as say, constructing a settler, a district, a builder, and a military unit.
I'll end this theory-crafting by emphasizing again that you're literally losing gains every turn any time you're not building a settler. The opportunity costs of this civic are not easy to measure, at all. Certainly not in a manner to declare it overpowered.
Of the economic civics, land surveyors seems to be the only potentially weak one.