'When Gutenberg invented the printing press, he took away the monopole of copying books from monks that were copying books by hand.'

But if you don't know how to write, It doesn't matter what tool you use. AI writes for you, if you want. It is only a probabilistic algorithm, and not a deterministic one. If you let the AI write for you, You won't have really written something. You will only have delegated the task.

In making backgrounds for your manga it doesn't matter how you helped the AI produce the result, if you don't have expertise in making comics or manga, your background can be beautiful but totally useless.
To make a manga you need multiple skills that you only get with experience and study. Making manga is a Japanese cultural process that goes beyond the comprehension of a Western imitation.
At the same time American, Argentine, French, Italian comics... They all have different rules and 'souls' that must be studied and understood.
"Making a manga with the AI" has no meaning, without the culture.

The culture and the skills are the real background in every human form of art.
AI is an algorithm.