I’m currently studying 19th and 20th century Japan, and I think the zaibatsu would be better represented as a replacement to the trading company rather than the factory. Zaibatsu were conglomerates of different industries, analogous to Amazon, Apple, or Disney nowadays, or perhaps the various East India companies of centuries prior. My suggestion would be to give Japan a conquerors event upon construction of the zaibatsu, but have the zaibatsu available 1-2 columns later than the trading company. This would also I think help alleviate how luck-dependent the Japan UHV is. Maybe have the event trigger war with China/Portugal/France (and their defensive pact allies) and spawn naval units? There’s probably other bonuses/maluses you could give the zaibatsu, but a factory replacement that gives commerce from water tiles is neither historically accurate nor particularly helpful imo.