In total the difference between the shortest (JP) and the longest (EN) is only about a minute.
Of course learning a language is more than just memorising stuff, you would also have to interact with the language regularly such as reading books, listening to music and watching videos in the targeted language, learning resources are only there to help you understand the language, you have to build your vocabulary bank and such through other means.
If it is as you stated that German and French localisations are better in your opinion, consider trying those 2 languages as they are easier than learning Japanese to a English speaker.
If you are dissatisfied with the localisation, you could ask for improvement of the localisation (such as why the tooltips of Sacred Soil and Passage of Arms can't be written normally as 10% mitigation like other 3 languages).
Telling people to 'learn Japanese' is simply a suggestion, I could even suggest a person that is satisfied with the EN localisation to learn Japanese and suggest them to try out the game in JP; suggesting people to try the game in JP (with the step of learning Japanese) is merely giving an option.
You specifically might not consider it as worthy of the effort you have to put in but some others might actually consider it as a good reason to start learning a language (I am mentioning this because you stated that you yourself are already playing in JP, hence this suggestion wouldn't apply to you specifically).