Out of the 4 policy cards that give +50%/+100% to yield, Rationalism is the best by far. Not only because it is easier to get +4 adjacency bonus with the Campus and the double adjacency card overall than other districts: Holy Site needs natural wonders (rare) or mountain range, Theatre Square needs to build up the bonus with EC/WP and wonders, and Commercial need a lot of effort with river and harbor.
Furthermore, the combined double adjacency card in the late game is widening the gap because the best one is Five-Year Plan (Campus/Industrial Zone) due to high focus on Science and how the Coal Factory works. It is followed by Ecnonomic Union (Commercial Hub/Harbor), mostly because of the Shipyard. Sports Media and Scripture can't rivalise.
But mostly because the policy is more rewarding due to Campus' building giving more yields:
- Library (+2), University (+4), and Research Lab (+3-8), for a total of 9 to 14 but -3 Power. Also, Hypatia gives +1 to Library, Isaac Newton +2 to Universities, and Albert Einstein +4 to Research Lab, increasing the maximum to 21 Science!
- Amphitheatre (+2), Museum (+2), and Broadcast Center (+2-6), for a total of 6 to 10 but -3 Power.
- Shrine (+2), Temple (+4), and Synagogue (+5) for a total of 11 but no Power consumption. Available way earlier, but no combined double adjacency cards.
- Market (+3), Bank (+5), and Stock Exchange (+4-11), for a total of 12 to 19 but -3 Power. But since Gold is at least twice as effective as the other yield, it is a "6 to 9.5" to yields.
I do not say that the Theatre Square and the Commercial Hub do not have value. On the contrary, but their value do not come from their building but more from the Trade Route and Great Works slots. Since Free Market and Grand Opera policy cards do not increase the Gold of trade route or Culture of Great Works, those policies would be less powerful than Rationalism.
If Rationalism is unbalanced, and need a balance, the balance shouldn't only come from making the prerequisite being harder to achieve, but also redirect the Science output from building to somewhere else, like:
- University: +2 Science, +1 Housing. Population in the city yields +0.15 additional Science.
- Research Lab: +2 Science, +4 Science additionally when Powered (3 Power). 1 random free Eureka at completion. (probably stupid and unbalanced suggestion, but I am throwing ideas)
Maybe something should be done for Hypatia, Newton and Einstein.