Sebastien LORBER you’re right.
I’ve read your issue at https://github.com/gatsbyjs/gatsby/issues/13806 and it seems there’s no immediate fix for that.
Unfortunately I don’t have much time to put into it at the moment but if you have some suggestion please let me know so I can update the article.
I’m subscribed to the issue so if anyone reaches any solution I’ll update this guide as well. Code-splitting should definitely be improved in my approach.