- "O ye who tread the Narrow Way, by Tophet-flare to Judgment Day, be gentle when ‘the heathen’ pray, to Buddha at Kamakura!"
– Rudyard Kipling
There are four Wonders with similar trope in Civilization VI, they all grant 20% of one type of yield to the parent city with one more secondary bonus. Ruhr Valley and Oxford University are great Wonders, Broadway is mediocre, but the Kotoku-in is absolutely underwhelming and almost never worth building.
The first bonus is 4 Warrior Monks. They are not "free", since you do not have to pay Faith to purchase them, but they still incur maintenance cost. The Warrior Monk is a terrible military unit for multitude of reasons, even in Classical Era, the era when it is unlocked, as it always gets outclassed by superior units of the same era. The Kotoku-in is unlocked a whole era later, these free Monks do not get any extra bonus, if they cannot be useful in the past era, they surely cannot be useful now. It is advisable that you should delete some of them, only keep 1 or 2 around for scouting purposes, if your exploration has been lacking. Otherwise, delete all of them, there is just no reason to keep around outdated military units that cannot be upgraded just to be put on Alert indefinitely.
The main bonus of this Wonder is 20% extra Faith for the parent city, which is underwhelming if you really break it down to see how much that actually means in number. Compared to Science, Culture and Production, sources of Faith are a lot rarer. Outside of unique bonuses, cities are likely to be dependent on Holy Sites and their buildings to generate Faith, and not much else. In Medieval Era, beside Ethiopia (the civilization with the highest Faith potential), no one else is guaranteed to have a city that can generate 50-60 Faith per turn, just to get 10 extra Faith per turn out of this Wonder. Also, considering the escalating cost of a lot of Faith purchases while Faith from Holy Sites and their buildings barely scale outside of certain policy cards, the Faith from this Wonder will never be meaningful enough to make up for it.
The bottom line is beside Ethiopia, you need a really good case for wasting 710 Production on this Wonder. The only usable bonus of this Wonder is the extra Faith, so the city to build this must have a good Faith generation and that Faith must have potential to scale. This condition applies only to Ethiopia, where their cities can expand to include new resources to be improved, and Trade Routes can always be sent from the Kotoku-in parent city, and since this Faith can get translated into Science and Culture, it is more like a 3-in-1 bonus. Certain civilizations like Russia (with Dance of the Aurora pantheon), Mali (with Desert Folklore pantheon), or Brazil (with Sacred Path pantheon) can generate a large amount of Faith very early, but since they almost exclusively rely on terrains and Holy Site placement (and its buildings), their Faith generation per city will not scale, thus this Wonder's impact will be short-lived.
Serene, enduring, and somewhat mysterious, the Buddha statue known as the Daibutsu sits outside of Kamakura’s Kōtoku-in. Towering over the Buddhist temple’s visitors, the Daibutsu patiently greets both faithful and tourist alike. An unknown artist cast the Great Buddha of Kamakura out of bronze, which has since oxidized into a muted green color through natural weathering.
However, the Kōtoku-in’s artist clearly built it to last. It survived an earthquake and two typhoons, one of which destroyed the building that used to surround it. The statue remains unfazed by nature’s attempts to unseat its 750-year meditation.