I really hate myself right now, because I'm still trying to make people understand the basic argument when I should just chalk it up to the reddit hivemind just saying 'no bueno' without having an actual counter argument. I mean I know responding here is a trap. No one is interested in the actual argument they just want to circle-jerk, but I'm going to try anyway because I'm a masochist.
I regret making mention to light novels and not being clear and concise in my original post because it has allowed people who don't like my supposition to simply ignore the argument and focus on other things which are based on opinion rather than basic facts about language and AI.
The bottom line is that you do not need to have a deep understanding of Japanese literature to perform a basic estimation of the number of valid sentence combinations.
Here are the facts: 1.) AI are able to easier solve problems which have a smaller number of possible valid answers. 2.) Due to having fewer words and more rigid sentence structure Japanese has fewer possible valid sentences than English. (I know you want to dispute this, I can feel it. Please do. I have all the facts I need to back this one up.) 3.) This is particularly salient in the realm of 'competent' prose writing for an AI which needs to explore more than just the first right answer, but instead needs to explore until it finds a 'good' answer. 4.) Having fewer possible answers to explore will allow the AI to choose a 'good' answer more often.
Therefore, because there are more possible valid sentence combinations in English than Japanese an AI will find the problem of writing 'competent' prose in English a harder task than writing 'competent' prose in Japanese. This actually has nothing to do with Japanese specifically, the same argument could be made for other languages with fewer possible valid combinations.
Beyond that my theory is that because certain aspects of Japanese prose are far more regularized then those same aspects in English the problem becomes even easier for the AI. Of course, 'easy' is a relative term (It's still a hellishly complex problem) but I'm only making a relative argument.
If you want to dispute my argument go ahead. If you just want to continue the circle-jerk then who am I to stop you?